If it doesn't install then the download is in the temporary folder and Ccleaner will clean that out. Before you try any more fixes and if you are on a laptop I suggest that you create your back to factory reset DVD discs or USB flash drive. Any repair carries a risk and if it goes belly up you can at least start again. Remember to backup all your docs, photos, music etc anyway.
Once you've created the restore medium and your backups, you could try a system restore to an earlier time and see if the update installs then.
Finding out how to create these restore mediums then Start page, right click a blank area, icon on bottom right, then you see all the tiles. Look for something like 'Recovery Manager', particular to your manufactured laptop.