Dude there are hundred's of threads all about Hyper 7 Upgrades.
Any standard size servo will fit in the Hyper 7, for example the Savox SC-1256 Coreless Digital Servo
Also good upgrades are: CNC Shock Towers, CNC Knuckles, CNC Uprights, Big Bore Shocks, wheels with a 17mm hex, any 1/8 buggy tyres and the rest of the list from here will fit.
And finally: http://tinyurl.com/3xho39a
Go Nuts!