Honestly if you can hold a screwdriver and get the correct ones its a 15 minute job that anyone can do on that machine.
Here is a very detailed guide for you.
https://www.ifixit.com/Guide/MacBook+Pro+15-Inch+Unibody+Mid+2012+Hard+Drive+Replacement/10761
If you have a hard drive caddy (or usb to sata cable) you can even use carbon copy cloner to create a complete copy of your current setup on the new SSD using USB and then just swap out the drives and off you go.
What of my bootcamp partition? Will that be copied too?