Space on mny external hard drive

On my computer regular hard drive I only have 220GB of space on my computer’s hard drive… I have used up most of the space even though everything is also backed up on my computer… However on my external hard drive, and I only clicked to save two files of everything… My hard drive is full.

Why is this?

Now can I run a disc defrag on my hard drive?? I know the options is are avaiable to use… but last year when I have many issues wiht my comuputer and my external hard drive. I tried to use those features, I evenn called your customer support center and I was told many things,… go ahead and use it., use disc clean  and I was also told not to use disc clean up…

Back in Deccemember when I did some of these functions… I was eventually locked out of my external hard drive and lost all the data on my external hard drive, as well as the data on my itnternal hard drive so will this happen if I defrag my external or do a disc clean up??

And again why do I not have anymore room on my hard drive?? Since I once had to safe 4 file copies of each for like 6 months and changed that in June… could I still have those files on my computer? and how do I take them off??? I really need ore space on my external hard drive and I know Iit sould be only half full at best but its up to 899GB HELP

What is the model number of the Hard drive?

I have a My Book Esssential sorry do not see a hard drive number…