A GTX 970 should put out a little less heat, but it's only a little faster, and IMO that's a lot of money to spend to produce a few fewer BTUs. Ditto switching to an Intel i5, although that'll be a much more significant performance upgrade over the Phenom than 970 vs. 770 and will naturally require a new MB. Last option is to get a high-efficiency (but not overpowered) power supply. A 550W Gold rated should work for your setup with headroom to spare. That's the cheapest option, but also nets you the least reduction in heat.
Now, this is the opposite of upgrading, but underclocking is always an option. And free!