Manual: page 105, 106
http://h10032.www1.hp.com/ctg/Manual/c04402649
Replacement of HDD needs major disassembly to be done. Get help from good technician if you're not confident enough.
Any 2.5 inch 7mm/9.5mm thick SATA internal HDD or SSD will be good.
Use Recovery discs/USB you should've created after first setup of this laptop, to factory reset OS after replacement.
You can take out HDD and connect it to another computer using SATA to USB adapter, then copy the files you can.
Regards
Visruth