I always use tools to do that,for example CClean, KeepPCSmooth etc. CClean is free,but it's only few features. So KeepPCSmooth can do that well.
The harddrive is the size of a standard notebook harddrive not a PC size harddrive. So you can not fit it in the smaller spot required for the notebook size harddrive
Try deleting programs you dont use and clean up some space on your harddrive and run ccleaner and clean the fans if its overheating.
You do not download the disc to harddrive you must purchase the game at the PlayStation store as a download to download the game to harddrive
depends on several factors- 1) if there is any data on that harddrive you need, TAKE OUT THE HARDDRIVE. 2) if the harddrive is less than 120 GB, and the above is not true, GET RID OF IT. 3) if the harddrive is working, and number 2 is NOT true, KEEP IT. A working harddrive of decent size is always helpful to have around.
A PS3 harddrive is a standard size notebook harddrive and are only worth the amount of a used laptop harddrive of the same GB size. The $50 extra currently being charged for the 320 GB harddrive is about value of a new 160 GB harddrive so a used 120 GB harddrive would be worth much less.
clean your harddrive
If you want to do your own harddrive recovery, you will need proper software to do it. Go online and download harddrive recovery software and try that. Hopefully, it will not need to be replaced.
You like to clean try disk kill or www.ultimatebootcd.com all so go to Harddrive maker free tool to fix test and help with harddisk.
PS3 has a Harddrive which you can change with a standard laptop harddrive
I would recommend buying a USB hard drive enclosure that will fit your harddrive.
On an internal HardDrive, or split across several DVDs
When it ask you if you wanna Save the game it'll ask you were and you pick harddrive.