Ouch. Lenovo is right up there with the worst when it comes to upgrades, the concensus being if you wanted bigger/better, you'd have bought it to begin with.
The v520 uses a proprietary psu, all 180w of it, with a maximum gpu of a GT730. Really pathetic for gaming beyond Microsoft Hearts. So a case swap will require a psu. You'll also need a 24-10pin main power adapter for the motherboard and some research done to figure out the front connector settings as that is proprietary too. May or may not need to do something with the cpu cooler.
It can be made to work, but isn't exactly easy as swapping aftermarket parts are. Most people just sell the complete pc and put the money towards a new pc