First of all you must learn basic .NET opcodes and identify your "jumps" (same as in ASM)
Here is some reference from M$ what opcodes do:
Code:
http://msdn.microsoft.com/en-us/library/system.reflection.emit.opcodes_members%28VS.71%29.aspx
but i am sure you can google for better list + HEX numbers ...
Process is the same: identify bad boy, examine offset, change HEX representative to NOP + correct PUSHed and POPed stack if needed