Upgrade processor iMac (mid 2010 specifically)

Yes, it is possible. By that I mean it is not physically soldered onto the logic board. However, as you mentioned, it will void your warranty. More importantly, Apple has not divulged the inner hardware workings of their system. Since Apple makes the logic board, and does not simply order stock motherboards, we do not know the exact number of chipsets that each physical board is designed to support. I have also heard that Intel sometimes will make the number of pins on Apple processors just slightly different than the PC version of the same processor.

All of that said, while it may be possible, it is not advisable, because messing up during an undocumented, unsupported process is more expensive than buying the new system.

I would definitely give it a try when you definitely want to upgrade - I mean: why not? Okay, it's a Mac, but I don't get the point why someone shouldn't upgrade or repair a Mac? Only because a lot of people who don't know much about computers prefer a Mac over Windows OS computer due to its simpler interface (and more uniform hardware) does not mean no one is allowed to touch it.

I never upgraded the processor so far (only RAMs and HD/SSDs), but I think this might be a good instruction for you. I guess this was something you were looking for...and yes, it looks like it is possible - even simple...but attention to the last sentence "Please note : Warranty is void with this step." ;)

http://www.ifixit.com/Guide/Upgrade+iMac+Intel+Core+i3+CPU+to+Core+i7/8670/1