If the computer is out of storage, with a drive as big as the one you mention.. something is fishy.
I have a drive that size the 1TB = 1 terabyte, which is a lot of space. I have so much on it that it is quite scary actually.
And still I have only used 1/2 of the space. It sounds like there is a lot of junk that may be taking up the space, that doesn't need to be there. I would first make sure that he goes through and cleans it up.
Run antivirus software, spybot, malware, adware, etc., software to make sure there isn't anything malicious taking up space. Then have him be sure he clears out his browser. Some people never think to clear the History, Cache and Cookies on a browser, but if you don't, they take up space quite quickly. Plus they leave you vulnerable to many issues. Just make sure he saves any pages he wants and also any passwords, etc., as when this is all cleaned out, things like auto log in and more will be removed and he will need the info to reopen those.
Then I would have him run Disk Cleanup and Defrag (both should come on the computer) and this will clean up more. The latter can take a 'while' to run.
If after all that, there is still no real room on the device, then it is time to consider what is being saved so you can determine if you need larger internal storage or just external storage. If it is things like photos, music, videos, etc., then you are probably better off with external storage that can be connected via USB and removed when not in use. This is also good for ZIP and other back up files as it has all the stuff you need, should the computer break down.
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