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?