Nextcloud using large amounts of space

I have a webspace of 50GB, the users are using about 18GB. Still my webspaceaccount has used 49.671 GB. So at the moment I can not upgrade my installation and can not really put any new files into it. I am aware that Nextcloud does versioning, but there should not be so much version fies. So I do not know what uses most of the space.
Can anyone point me to what to do to find out where the space is used and how to reduce the usage safely? Unfortunately it is just webspace, so no SSH, just FTP available.

Do you have preview generator activatet and an amount of grafic-files on your instance?

doesn’t your webhoster have a web-ftp Interface that shows you what directory is using how much amount of storage?