Navigate to your COD folder and enter the MAIN directory.
eg. c:\Call Of Duty\Main\
Edit the config.cfg or config_mp.cfg file in notepad or similar
Find and change the following lines …
seta r_customwidth "1920" seta r_customheight "1080" seta cg_fov "96" seta r_mode "-1" seta com_introplayed "1"
Save the file(s) and restart COD. Do not manually change the video options within the game otherwise it will undo your changes.