It's not just a matter of popping it in. 99% of the time there are special heat dissipation mechanisms involved because the tight quarters of a laptop chassis. This also means that usually the CPU is soldered on. Even if you did manage to get it out and an i7 in, laptop model processors are difficult to find because it's a dumb idea to switch them out. Let's say you did find one and replace it, you're likely to face a whole world of power consumption issues depending on which model you end up with. Laptops really aren't designed to accommodate anything other than what they come with (exceptions being RAM and hard drive, in some cases GPU), so the on-board PSU is really only equipped to handle stock components.
I'll be honest with you though unless you're doing CPU-heavy work like feature film editing then you wouldn't even notice the difference between an i5 and an i7 unless there's a vast clock speed improvement between the models, or you jump chipsets (which would likely require a motherboard replacement anyway).