Would a carbon fiber fork make a significant difference? I have a Giant Escape 2012 that i love.  I ride it more than my road bike. Ive recently switched from 32mm to 28mm tires and can notice the improved handling and speed. Is a carbon fiber fork a good upgrade? I'm mainly looking for upgrades to make my bike lighter. Also, what size would I need? I cant find my bike specs online.
No, it is not a good upgrade.

The fork change could save some weight, up to about 400 grams. This is less than difference between full and empty bottle. The ride quality may or may not change depending on your current fork and the replacement. 

If you can't look up the specs of your bike, you can always measure yourself, the critical measurements are steerer tube diameter, steerer tube length (new forks come with extra and you are supposed to cut them, just don't get too short one) and distance from fork crown to axle.