You're downloading SOMETHING from MEGA with a 4 GB file size?

You're not... PIRATING anything, are you?

But seriously, try CCleaner.

delete die file?

delete the file from your download folder.

this guy ...

the file isnt in my Download folder because it said disk was full when its not

Are you using Megasync?

Use Chrome. It is the only browser that works for me when using mega with big files
And try the things people already said for recovering your space

nevermind, misunderstood something

clear your browser cache, also windows temp files (easier to do it with ccleaner like kukke suggested).

if everything fails, reinstall windows :3

You drive might have a bad sector and might have issues accessing that and hence why it can not be deleted or the file you downloaded may be protected from being deleted.Like it has write protections.

Can you take a screen of what happens when you try delete or tell us what happens,like do you get access denied or something like that?

I am not saying you are but if your doing what some have joked about it not always wise as people like to infect those files or make fakes files to waste your time I am just assuming here either way that what you download is a movie given the exact size of the file or whatever it is takes up one dvd.

Okay, this may not have anything to do with your problem with mega, but...

GUESS WHAT THE DAILY STEAM SALE IS TODAY!!!

Are you downloading stuff while you don't have the space on your computer :D ? Remove some steam games and try again...

Look in your desktop, sometimes MEGA stores the downloads there

It's probably temp files, so restarting or using the windows system cleaner dialogue might help. Alternatively, you could try clearing the browser cache, since I think that's how Mega stores its temporary download files.