I take a lot of photos. iPhoto has 45,000 of my best ones, and my old MBP could not hold them. I found I was just no longer using it. A new computer just to add more HD space? NOT cost-effective. I don't need speed, I just need ROOM.
A new 1TB drive is only $110. I cloned my existing system to the new drive using an external FW box I already had, then checked ifixit for the process...
Hm. Intimidating. I had almost everything I needed. My "tiny torx" set included only even numbered bits, but usually the next size down can handle an odd screw.
So I launched into it- nothing ventured, nothing gained. Getting the keyboard off was a bit stressful- the sounds were identical to what you hear when you break things. I got the tiny connectors apart, pried off the cables glued securely to the inner workings, and got down to the actual HD clamps, the ones that are fastened with #5 torx. One came off with a #4 and one did not. The last screw. Don't it always seem to go... So, I could buy just the 1 #5 torx driver, or I could buy a set of just about every driver I could ever need (for about the third time- the definition of "need" keeps changing!) for about twice the amount. So naturally I went for the latter.
Gosh, the right bit actually works, and now so does my laptop!
With reassembly you need to pay attention to where the cables and parts "want" to go, and keep the screws in separate places for the different stages of dis/assembly. I laid them out according to where they went- a pile on the left for the left case screws, on the right for the right case screws, etc. Front to back was the sequence of removal, the first out are the furthest back, the closest are the latest removed.
This was an intimidating process- swapping out a HD in an older aluminum MBP. But the instructions are good, and if you take your time (and pay attention) you will be OK.