I Just deleted a bunch of files (including that blender file you mentioned), downloaded all remaining files and made a local backup and then deleted almost everything in the project. The download accounted for about 290MB.
Now i can upload files again, but when i upload 1 more .glb file of my robot model my disk space seems to be full again. Just out of curiosity, how much disk space do i have exactly? I can't seem to find any information on that.