How to upgrade Android on the Samsung Galaxy Ace
You certainly can upgrade your OS, although the process isn't without risk.

There's an entire board devoted to the Galaxy Ace at xda  - here's a good post which should get you started.  From the quick skim I've done over a few posts there seems to be a massive warning of not to use ROM Manager (a popular tool in the ROM community) as it'll brick your device.  

Once your device is rooted you can then install a ROM - here's a link to a Cyanogenmod 10 based ROM for the ace running Android 4,1, I think.  Be careful to read the instructions and take note of the stuff that doesn't work. If you get stuck - there's lots of help out there

Good luck.