I really doubt you can install that HD 7970m. The vast majority of laptops have the graphic chip soldered into the motherboard. Laptops that can potentially be upgrade are gaming laptops to begin with and usually start at $1,500+.
Those gaming laptops may have an MXM slot (types I, II, III; the higher the type the thicker the card) which can be used to install a MXM format graphic card as long as the slot is big enough for the card. The Radeon HD 7970 is a type III card. Even some gaming laptops with MXM slots will have the graphic card soldering in so that no upgrade is possible.
There's no way in hell will a budget oriented laptop like the Compaq Presario CQ57 will have a MXM slot in it.