Every channel has a space where any files shared in that channel are collected.
The section “Shared files” can be found in the channel-information. These can be opened by clicking on the 
You can also directly upload files in the shared files and you can create folders to organize the storage.
The channel manager can move/delete any file, regular members can only move/delete their own files. Deleted files will be deleted from the chat history if they were sent there.
The storage space needed to store the file is deducted from the person who uploaded the file.