Can I put 2 voltage regulators (5V) in parallel to dissipate the heat better?
No, but depending on what your power source is you may be able to do 2-stage regulation to spread the heat - for instance, if your source is 12V then lower it to say 9V first with a 7809 then drop it from 9V to 5V with the 7805.  If you're even higher than that, then you could use a 7812 first to drop to 12, then the 9V, then the 5V.

Either that or just use a switching regulator, such as a UBEC used by RC vehicle enthusiasts (available for a couple of $ from eBay or most RC model shops).