How do I relocate my bitcoin data in bitcoin-qt to save space?
I recommend reading about the Bitcoin Data Directory.  You should also take a look at this answer:  How do I specify in which directory Bitcoin blocks and other data should be stored?

Basically, all your Bitcoin data is stored in ~/.bitcoin on Linux.  Not only can you specify a different location for this directory using -datadir=/some/other/directory, but you could also symlink ~/.bitcoin to some other directory on a secondary disk or network share, like this:

ln -s /some/other/directory ~/.bitcoin

However, from personal experience, I would suggest not using a network share.