you could try a simple google search...or being quite kind...ive done it for you
you could use this app
https://play.google.com/store/apps/details?id=com.manniakk.cscselector
OR this app
https://play.google.com/store/apps/details?id=com.laucass.sgscsc
OR
CSC How to change CSC Samsung S2 Galaxy
1. Just type * 272 * #IMEI on the phone device. (find your imei on the box or type *#06#)
2. Choose a CSC that you want.
3. Click Install.
4. Phone restarts itself.
***Be Warned - doing this WILL factory reset your phone***
Try the apps mentioned in this post
Sent from my GT-I9100 using xda premium