Did my 2010 i3 a few months back . You'll need a pair of suction cups to get the cover glass off , and some Torx drivers to get the LCD off . I found that the hard part was disconnecting the LCD cables , I've got big hands and there's not a whole lot of room between the panel and the rest of the computer . There's 4 cables to disconnect . The 2 left arrows come off pretty easy , the third arrow is the LCD temp. sensor , be careful with this , or CAREFULLY peel it off the back of the lcd . The socket that's circled is the worst , it's real fragile . To get the cable off , there's a pull tab which releases a cable lock, this lock needs to be rotated up toward the top of the computer and then the ribbon cable needs to be pulled vertically (to the top of the computer , not toward you) out of the socket , without lifting away from the logic board. Once the LCD is off , the rest of the job is straight forward . Just be REAL CAREFUL reinserting the ribbon cable , it goes in flat ,don't angle it .Remember to reclip the cable lock . Get the same brand HDD as you have in the machine. Just know that aftermarket HDD's don't have Apple's embedded fan speed software, so upon reassembly and OS installation , the HDD fan will run full speed , download a copy of SSD fan control ( its free)and run it in SMART mode , this will control the HDD fan and quiet things down . Just know that it doesn't control fan speed under Boot Camp , so if you need Windows , use Parallels , or VM Ware
Take your time , look over the iFixit directions a few times and make sure you have a well lit , quiet area to work in . Good Luck!!