I keep deleting files but my Macbook Pro hard drive is still full I have a MacBook Pro (late 2011) with a 500Gb SSD hard drive.

Today suddenly it said that my hard drive was full, so I started removing the files. Got rid of lots of Gigas, even the sleepimage file, emptied all the trashes, etc. 

Still, it shows like nothing was deleted, only has 500 Mb free and nothing is changing.

Do you know what the problem could be?
Probably TimeMachine local snapshots is enabled on your Mac. Local snapshots are basically backup files stored on your local hard-disk (as opposed to regular ones stored on the external TimeMachine volume). This is a useful feature for people who travel a lot, so they can revert files to recent versions even when they are not connected to their home TimeMachine.

To disable "local snapshots" open Terminal and enter sudo tmutil disablelocal and hit ↵.
Enter your password at the prompt (the password  will not be visible) and hit ↵ again.
Enter exit, hit ↵ and quit Terminal.

Now check in Finder and Disk Utility if you regained valuable disk space.

To reenable local snapshots just enter sudo tmutil enablelocal.