You'll have to let us know what iMac you have, try Everymac.com, and link us to the exact model you have.Will an iMac take a 7410? They can handle a 7400 though.
I think, any 7400/7410 are pin compatible, so if you can upgrade to a 7400 you can upgrade to a 7410.
You really need to look at the threads about how @dosdude1 and @LightBulbFun do their cpu rework, they are not trivial swaps, and they have basically rolled their own SMD rework stations.
Back in the day, a few companies offered these CPU reworks, but they had the equipment, including X-Ray machines that they could check the flow of the balls between the CPU and the pad when something went wrong.....
It's really fun and cool to play with these old systems, but it becomes an addiction, and before you know it you have thousands of dollars wrapped up in old Macs, and the only way to get your jones is to buy more hardware
Being as how you are 13, I'd say spend your time learning to code, there isn't really much money in hardware, however good or great coders can name their price. I know you didn't say you were doing this for money, but having money helps to buy all the equipment we love to play with.