As we all know Debian is a very stable Linux distribution which is partly what makes it great, sometimes however you want access to newer packages, while it’s possible to mix stable packages and unstable it often leads to quite a mess, some packages have so many dependencies it’s often easier just to go entirely to unstable.
Unstable despite its name is actually fairly stable for the most part, so upgrading to it isn’t usually a big issue, upgrading is best done as a two step process, first from stable to testing, then testing to unstable, trying to go directly generally will not work except for a freshly installed base system, for you average user I’d recommend stopping at testing and then just install what you need from unstable since package problems can and do occur.
First you need to edit /etc/apt/sources.list and change jesse to testing like so, use a mirror closest to you for best performance:
deb ftp://ftp.uk.debian.org/debian/ testing main
deb-src ftp://ftp.uk.debian.org/debian/ testing main
deb ftp://ftp.uk.debian.org/debian/ testing contrib
deb-src ftp://ftp.uk.debian.org/debian/ testing contrib
deb ftp://ftp.uk.debian.org/debian/ testing non-free
deb-src ftp://ftp.uk.debian.org/debian/ testing non-free
Once that is done run the following:
sudo apt-get clean
sudo apt-get update
sudo apt-get dist-upgrade
All being well there should be no package errors here, go ahead and let it upgrade to testing, once it’s done it’s best to reboot and make sure everything is working, in some cases you may have to reinstall your gpu driver.
Once you’re happy everything is working you have two options, you can stay on testing and add the unstable repositories, or dist-upgrade to unstable, to get the latest packages you want, you can use the -t switch with apt-get, aptitude and synaptic to select the target release for example:
sudo apt-get -t testing install some-package
sudo apt-get -t unstable install some-package
sudo synaptic -t unstable
There is also an option in synaptic to set your preferred release.
If you do dist-upgrade to unstable be aware things can break from time to time, mostly packages that are being worked on, fixing this is a simple matter of switching whatever is broken back to the testing version, if you’re not comfortable with doing this stay on testing.