Two articles with good step-by-step:
Backed up here: How to root the Samsung Galaxy Ace 2 – CNET + How to install Jelly Bean on the Samsung Galaxy Ace 2 – CNET
I have instead of Jelly Bean installed 12.1
I ended up with good install after first try. First booting took minutes.
I have also problems right now: phone vibrates/freezes for a second every two minutes + I can’t call
Newer but may be buggy:
Cyanogenmod walkthrough that did not work for me: