Example of removing side borders on C64
See my answer to "How do I show sprites in the border on C64" which contains the assembly code to remove the side and bottom/up border together with how it works.
Example code can be found on 'codebase'...
http://codebase64.org/doku.php?id=base:removing_the_sideborders
http://codebase64.org/doku.php?id=base:sprites_in_bottom_sideborder