Editing and pasting on server

[CaioMS2000]

I need to make an edit in the schematics. The build is in the water, so I wanted to remove only the parts that are water and keep just the blocks. Is that possible?
Another thing that's happening: I can't use the paste option on a server. Do I need to do something to make it work? On the server, when I use the stick, I can only access the options "Edit," "Placement," and "Area Selection."