I'm not a coder, I need to change a checksum of an .exe file,
Is there any guide about it, idealy it would be if someone can do this for me.
Thank You.

You can't... easily.

Are you trying to change the checksum of an executable in order to obtain the original checksum (so you can hide file changes), if so you are out of luck as I doubt you have the processing power to obtain this.

The attack requires brute forcing to collide the hash.

A full answer can be found here: http://stackoverflow.com/a/1756131/1161270

In other means, no you will not be able to do this.