Freeing up disk space

Delete any temp. files along with anything else you really don't need.

use a flashdisk to transfer some big files off the hdd, use disk clean up tool from windows or use a cleaner software like piriform's ccleaner, defrag, put the files back in. you can disable your page file and hibernation file to free up more space and defrag the spce both files occupy.
you can use alternative defragging softwares like piriform's defraggler. iirc defraggler lets you defrag individual files.(imo both ccleaner and defraggler both are good at what they do)

If you have enough RAM, lower the pagefile or disable it.

Disable hibernation.

Disable system restore.

Lower the amount of space allowed for recycle bin.

Do disk clean up.

Use cleaning program, e.g. CCleaner to clear out cache and temp files. Uninstall unused window features and programs.

Move files to other storage drive.

I'm currently using the Piriform Defrag. Going slow.

when you defrag, make sure the files that are being moved by the defrag prog are not in use by other program e.g. anti virus. you can raise defrag program's priority if you want (from task manager or the program itself) or temporarily lower anti-virus' priority(but do not disable the anti virus). if the defrag prog tries to move/defrag a file that is being used by another program, it'll stall or slow down.

Delete programs or files that you no longer use to free up disk space.

Transfer important files to an external hard drive or burn them onto a DVD disc.

Purchase and install a larger hard drive.

buy more hard drives and big memory sticks.

try ccleaner and glary utility to clean temp files ,cookies,obsolete registery keys

backup everything you need off the main disk and reinstall everything! mmmm fresh install