I found one in Walmart, is it easy to install? and can i move the save data from my old hard drive to the new one?

Not sure about moving save data, but installing the hard drive is relatively easy. If its an older ps3 you're referring to, there's a little thing on the left side that you can pop off. You'll see a blue screw on the hard drive. Unscrew it, and pull the little tab so you can grab the hard drive. Slide the hard drive to the right, you'll hear a click, and you can just pull out the hard drive.

Very easy, pry off the cover, then slide out the HDD. Take the blue screw out then swap the HDD. Backup to an external HDD first using the backup manager doing in settings