First, install CWM recovery
1. Download this file http://www.mediafire.com/?3umwbz3gg6oo6c6
2. Put this in root of ur sdcard
3. Go to recovery by Powering Off your phone then press Home+Power button until you see the recovery
4. Go to "update from sdcard" then go to signed_cwm-188.8.131.52-flashablezip-ext4+rfs.zip (Navigate using Volume up and Down(Going Up and down) Home button(For ok button)
Final step is to Install a rom!
How to install a rom?
1. Download your desired rom
2. Download ext4-formatter.zip http://www.mediafire.com/?8p6s9mlpqwowq51
3. Go to Recovery by pressing (Home+Power) buttons
4. Wipe data and cache
5. Wipe Advanced davlik cache
6. Go to "install from sdcard" then go to ext4-formatter zip (Navigate using Volume up and Down(Going Up and down) Home button(For ok button)
7. Go to "install from sdcard" then go to rom file.
5. Reboot(First boot will take some mins)
If your rom didnt have preinstalled Gapps in your ROM and need to install it heres the steps to do it!
1. First download the Gapps for the required ROM e.g for cm10.1 u need cm10.1 mdpi gapps. you can find them at http://wiki.cyanogenmod.org/w/Gapps
2. Copy the Gapps to Sdcard
3. Reboot into CWM Recovery and go to mounts and storage then mount system
4.Go to install zip from sdcard then go to choose zip from sdcard.
5.Install the Gapps zip