Hard drive full und docker not running

I do have 12 sites on my server running. Today I got an error message 521. In the I do think the problem is that the hard drive is to 100% full. So docker is not running anymore. So I was trying to delete on website with sudo ee site delete mydomain.com , but I got the message Docker not installed or not running. So I connected with Filezilla to the server and was trying to delete the Folder of mydomain.com, but there I do got the message access denied.
So who can I delete one domain? or how can I get a little space on my hard drive so docker und the easyengine commands are working again.
Sorry for asking proberly something very simple but I am not a computer wiz.

Thanks in advanched for any help