com_hunkMegs sets the allowed memory for the graphics of the game.
/seta com_hunkMegs 256
Values example: 64, 128, 256, 512, 1024 (of course it can be between them, higher or less also)
Don’t use more than 3/4 (75%) of your actual memory in your computer.
Usually 256 or 512 is fairly enough, even for the most complex enemy territory map graphics.