I've noticed a lot of people getting stuck with the ROMs and I've had a few PMs about a post I made a while ago. I'd like to start by saying most ROMs are for the S5830 only, not the S5830i - if you try with an incompatible ROM you will get the dreaded boot loop. The solution to these boot loops is often confusing and scattered among many threads, this is my attempt at getting a simple guide into one thread.
If you have any questions please ask here rather than PM.
1. First thing you need to do is have the Samsung drivers, if you're on Windows 7 or above, Windows can probably go find them for you when it comes to plugging your phone in. If not, Kies is available on Samsung's site here which includes all of the drivers required.
2. You need to have the original stock firmware, luckily they are essentially all the same so here is the Open Australia version I used (I'm on O2 in the UK) http://www.mediafire.com/?903oq9l7qbmkir4 (password is: mod2xtreme.com)
3: Extract that folder somewhere you will remember.
4: Odin is a firmware flasher, it's what will save your phone. It needs a PIT file, luckily some kind person has already packaged the PIT for the Ace within Odin here: http://forum.xda-developers.com/show...3#post49343353
Now you have all the different pieces required
5: Open Odin on your computer and put your phone into Odin mode by holding the power button, volume up and volume down. (and read the screen, it'll ask if you if you're sure and to press volume up) - once you plug the phone in correctly and the drivers are installed Odin should come up saying "<ID> Added!!"
6: A picture paints 1000 words here: http://i.imgur.com/La1r4zE.png - you should ensure you select your PIT file, and all the correct files from step 3 (modem = phone) - click start then wait for it to say "Pass" (I had a nervous smoke here)
7: Boot your phone into recovery by pressing the home button, volume up and power. Let it run through the update and wipe the cache and reboot itself.
8: You're in! It went German on me so I had to change the language at the startup screen, but other than that it's fine.