I was using Win 7 on a 120GB SSD from Corsair. I had like 38GB free before i upgrading to Win 8. Before upgrading i only have the OS and GW2 game on it. After i upgrade to Win 8, my SSD free space went from 38GB to 18Gb O.O. I am worry right now, where all the other space goes?
Windows only needs about 20-25 gig roughly depending on your configuration. If your SSD is that full, it may be time to move some stuff to another drive, ya think? Understand that also if you did an inplace upgrade, all your old files and windows installation will saved under a file called something like "windows.old", and it can easily be 100 gig.
Usually upgrading from one Windows version to another is not what I would recommend based on my personal experience. First, the system is never as fast and responsive afterwards compared to a clean install and merging the old registry to the new ones increases the chances to get weird bugs, etc... Also it kept a lot of files that it doesn't need from the previous Windows 7 so this is probably why you lost a lot of space.
As others already mentioned, my only advise would be to format the drive and reinstall Windows 8 with a clean installation. Also look at Cin19 advises to better optimize your OS for SSD and also save additional space. Another thing you could disable is the automatic defragmentation, I heard that SSDs don't need it and it would only reduce its lifetime.