First update all your packages
Code:
apt-get update
apt-get upgrade
apt-get dist-update
Make sure you stop all important services (apache, nginx, mysql, etc.)
Then update your OS to Debian 8 (8.6 is the latest)
Code:
nano /etc/apt/sources.list
Replace any repos for wheezy with jessie (debian 8)
Code:
deb http://ftp.us.debian.org/debian/ jessie main
deb-src http://ftp.us.debian.org/debian/ jessie main
deb http://security.debian.org/ jessie/updates main
deb-src http://security.debian.org/ jessie/updates main
# jessie-updates, previously known as 'volatile'
deb http://ftp.us.debian.org/debian/ jessie-updates main
deb-src http://ftp.us.debian.org/debian/ jessie-updates main
These other 2 repos showed on my sources.list when I had installed Debian.
Code:
deb http://httpredir.debian.org/debian/ jessie main contrib non-free
deb http://httpredir.debian.org/debian/ jessie-backports main
Refresh package list and update important packages
Code:
apt-get update && apt-get install apt dpkg aptitude
Then update all packages again
Finally reboot
. It's a long process, but old OSes aren't supported.