Before you can flash/install CUSTOM ROM for Samsung Galaxy W GT-I8150,
You need to :
1. Root your phone. Click here to root if you haven't yet.
2. Install ClockWorkMod (CWM). Click here to install it if you haven't yet.
How to flash/install CUSTOM ROM for Samsung Galaxy W GT-I8150 :
1. Download the rom you want to flash. Example: you can download this one.
2. Copy the zip file (the rom) to the USB Storage. If you downloaded the file in parts, you need to extract it (using 7zip) into only 1 zip.
3. Boot into ClockWorkMod ( Press volume up+menu+power button and release power button when samsung logo appear. )
4. [Optional] Backup your current ROM using nandroid (just in case).
5. Install the zip file (the rom) [choose the rom in the sd card]
6. Restart your phone.
First boot after install a rom usually takes longer than usual. So, please patiently wait.