hi, i have a 1.8T 180bhp leon, i would like to remap myself but have some snags

1.can i remap via obd2 port (i have already copied original to pc via the obd2 port)

2.how do i modify original file. i have ecm2001 and have been told its easy, however im not sure and dont want to continue without being sure
3. do i have to do something with the checsum as some say important
basicly as u have guessed im new to this stuff but have read others who have managed there own. want to edit mine as i dont trust modified maps from a disc that cost 2 quid!