How to upgrade selected packages

It is very easy to upgrade the whole Debian system, but you can also upgrade only selected packages and skip the rest.

List available updates by simulating upgrade process.

$ sudo apt-get upgrade -s
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be upgraded:
  gnupg gpgv libgcrypt11 libssl-dev libssl-doc libssl1.0.0 linux-headers-3.2.0-4-amd64 linux-headers-3.2.0-4-common linux-image-3.2.0-4-amd64 linux-libc-dev openssl
11 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Inst libgcrypt11 [1.5.0-5+deb7u4] (1.5.0-5+deb7u5 Debian-Security:7.0/oldstable [amd64])
Inst libssl-doc [1.0.1e-2+deb7u21] (1.0.1t-1+deb7u1 Debian-Security:7.0/oldstable [all])
Inst libssl-dev [1.0.1e-2+deb7u21] (1.0.1t-1+deb7u1 Debian-Security:7.0/oldstable [amd64]) []
Inst libssl1.0.0 [1.0.1e-2+deb7u21] (1.0.1t-1+deb7u1 Debian-Security:7.0/oldstable [amd64])
Inst linux-image-3.2.0-4-amd64 [3.2.81-1] (3.2.81-2 Debian-Security:7.0/oldstable [amd64])
Inst gpgv [1.4.12-7+deb7u7] (1.4.12-7+deb7u8 Debian-Security:7.0/oldstable [amd64])
Conf gpgv (1.4.12-7+deb7u8 Debian-Security:7.0/oldstable [amd64])
Inst gnupg [1.4.12-7+deb7u7] (1.4.12-7+deb7u8 Debian-Security:7.0/oldstable [amd64])
Conf gnupg (1.4.12-7+deb7u8 Debian-Security:7.0/oldstable [amd64])
Inst linux-headers-3.2.0-4-amd64 [3.2.81-1] (3.2.81-2 Debian-Security:7.0/oldstable [amd64]) []
Inst linux-headers-3.2.0-4-common [3.2.81-1] (3.2.81-2 Debian-Security:7.0/oldstable [amd64])
Inst linux-libc-dev [3.2.81-1] (3.2.81-2 Debian-Security:7.0/oldstable [amd64])
Inst openssl [1.0.1e-2+deb7u21] (1.0.1t-1+deb7u1 Debian-Security:7.0/oldstable [amd64])
Conf libgcrypt11 (1.5.0-5+deb7u5 Debian-Security:7.0/oldstable [amd64])
Conf libssl-doc (1.0.1t-1+deb7u1 Debian-Security:7.0/oldstable [all])
Conf libssl1.0.0 (1.0.1t-1+deb7u1 Debian-Security:7.0/oldstable [amd64])
Conf libssl-dev (1.0.1t-1+deb7u1 Debian-Security:7.0/oldstable [amd64])
Conf linux-image-3.2.0-4-amd64 (3.2.81-2 Debian-Security:7.0/oldstable [amd64])
Conf linux-headers-3.2.0-4-common (3.2.81-2 Debian-Security:7.0/oldstable [amd64])
Conf linux-headers-3.2.0-4-amd64 (3.2.81-2 Debian-Security:7.0/oldstable [amd64])
Conf linux-libc-dev (3.2.81-2 Debian-Security:7.0/oldstable [amd64])
Conf openssl (1.0.1t-1+deb7u1 Debian-Security:7.0/oldstable [amd64])

Install updates, but skip these related to Linux kernel.

$ apt-get install --only-upgrade libgcrypt11 libssl-dev libssl-doc libssl1.0.0 linux-libc-dev openssl
Reading package lists... Done
Building dependency tree
Reading state information... Done
Suggested packages:
The following packages will be upgraded:
  libgcrypt11 libssl-dev libssl-doc libssl1.0.0 linux-libc-dev openssl
6 upgraded, 0 newly installed, 0 to remove and 5 not upgraded.
Need to get 5857 kB/6158 kB of archives.
After this operation, 265 kB of additional disk space will be used.
Get:1 wheezy/updates/main libssl-doc all 1.0.1t-1+deb7u1 [1224 kB]
Get:2 wheezy/updates/main libssl-dev amd64 1.0.1t-1+deb7u1 [1791 kB]
Get:3 wheezy/updates/main libssl1.0.0 amd64 1.0.1t-1+deb7u1 [1283 kB]
Get:4 wheezy/updates/main linux-libc-dev amd64 3.2.81-2 [858 kB]
Get:5 wheezy/updates/main openssl amd64 1.0.1t-1+deb7u1 [700 kB]
Fetched 4735 kB in 2s (1990 kB/s)
Reading changelogs... Done
Preconfiguring packages ...
(Reading database ... 58380 files and directories currently installed.)
Preparing to replace libgcrypt11:amd64 1.5.0-5+deb7u4 (using .../libgcrypt11_1.5.0-5+deb7u5_amd64.deb) ...
Unpacking replacement libgcrypt11:amd64 ...
Preparing to replace libssl-doc 1.0.1e-2+deb7u21 (using .../libssl-doc_1.0.1t-1+deb7u1_all.deb) ...
Unpacking replacement libssl-doc ...
Preparing to replace libssl-dev 1.0.1e-2+deb7u21 (using .../libssl-dev_1.0.1t-1+deb7u1_amd64.deb) ...
Unpacking replacement libssl-dev ...
Preparing to replace libssl1.0.0:amd64 1.0.1e-2+deb7u21 (using .../libssl1.0.0_1.0.1t-1+deb7u1_amd64.deb) ...
Unpacking replacement libssl1.0.0:amd64 ...
Preparing to replace linux-libc-dev:amd64 3.2.81-1 (using .../linux-libc-dev_3.2.81-2_amd64.deb) ...
Unpacking replacement linux-libc-dev:amd64 ...
Preparing to replace openssl 1.0.1e-2+deb7u21 (using .../openssl_1.0.1t-1+deb7u1_amd64.deb) ...
Unpacking replacement openssl ...
Processing triggers for man-db ...
Setting up libgcrypt11:amd64 (1.5.0-5+deb7u5) ...
Setting up libssl-doc (1.0.1t-1+deb7u1) ...
Setting up libssl1.0.0:amd64 (1.0.1t-1+deb7u1) ...
Setting up libssl-dev (1.0.1t-1+deb7u1) ...
Setting up linux-libc-dev:amd64 (3.2.81-2) ...
Setting up openssl (1.0.1t-1+deb7u1) ...

This command will upgrade only installed packages, it will ignore non installed ones.