There is ROM made by some guy name x-treme. I must tell you that it is a NON-OFFICIAL ROM. So, if anything doesn't work then only you are responsible.But this is just to say. There are plenty of people to help you :D. Personally, I have been using the rom since like a week now and I haven't noticed any kind of major bug myself.
First you gotta root your S2. There are tons of tutorials for that on the internet including video ones.
Secondly, you gotta make a backup.
For contacts backup I, personally sync all my contacts to google so there is never a problem of losing any contacts.
You don't have to worry anything which is on your SD card.
Then you gotta make a phone backup incase anything goes wrong. I recommend titanium backup or anything. Make with 2 apps just to be sure.
Then head over to x.da and download the rom. Then flash it to your phone. If you are doing it for the first them then tell me. In that case, I'll write a step by step custom tutorial for you
Happy rooting

Regards,
Nitish.