Reducing the size of content within a composition in After Effects
You can scale down everything in your composition by pre-comping everything and then shrinking the size of that pre-comp. I'm not entirely sure what you mean by "when I adjust the comp size the footage stays the same". If you mean that when you change the composition size, the footage extends beyond the new border of the comp, then pre-comping and scaling down the pre-comp should fix this.