Help to flash a Samsung GT-B2100i

Hi All,
I am new to flashing mobile phone, and am in need of assistance.

I have a Samsung GT-B2100i which is showing

!!! Blocking Defence
1. Error Code: 0XBD020401
2. Version: B2100IXXMD5
3. Error File:
4. Error Line: 0
5. Ramdump State

I have been told it needs to be re flashed. I have bought the USB computer lead, but have no idea what I need to download to actually flash the phone now.

Can anyone help me please?

Many Thanks