Feasible to upgrade processor in iPhone 4?

I don't mean to sound rude, but I'll just be honest when I say that you're barking up the wrong tree here. There really is no way to upgrade an iPhone of any model. They're just not a device that was meant to be upgraded. The only option to upgrade an iPhone in any way would be to install a motherboard of the same model with more storage. In other words, you could replace your 16 GB iPhone 4 motherboard with a 32 GB version. Of course, that wouldn't help with performance, it would just give you more storage.

If if upgrades were possible, they would be cost prohibitive. Heck, even just a straight replacement motherboard for your iPhone 4 right now would cost nearly as much as replacing the phone.

You mention that you're looking to "speed it up". Have you done a restore of the phone and set it up as a new phone lately? Doing that periodically will keep the phone running at its best, as this gets rid of any clutter that has built up in the depths of the operating system that you can't see.

No. You can't. Sorry. I was thinking exactly the same, and, i wrote this comment ON MY LAGGY IPHONE 4. But, to the point. If you want a faster phone, you could try to turn off your motion graphics, and increase contrast. Also, turn off background app refreshing. It helps. And, if you really want to get a faster phone, you may risk a A7 processor and edit the whole board to the pin layout for the iPhone 4. But its not worth of it. Im looking for some money to buy a 5C or 5. But yeah, i know how you feel holding the slowest phone on the world(not really, just a slow one). Sorry, the tips i gave you are the only ones that give effect, espeshially for gaming.

I replaced the cpu in my iPhone 4s with one from a busted iPhone 6+ my friend had. Just used an exacto knife (while powered off obviously lol) and cut to size, popped the motherboard in my 4s and plugged it in. Don't let these guys discourage you. It wasn't that hard and the performance increase was HUGE.