Only admins with the permissions to delete will see this Remove option.

If you no longer need a file within the library you can Remove it from the folder(s) it resides. This will remove the file from that location and be stored in the trash for 30 days, after which it will be permanently deleted.  

Removing a single file:

1. Hover over the file you wish to remove with your mouse to bring up ... Icon and click.

2. Click the Remove button.

3. Click Remove in the confirmation modal.

Note that a file Synced to multiple folders will be presented with a warning that you will be removing from all locations, if you choose to just remove from a single folder, just select the folder(s) you wish to remove from. 

Via Selection:

Note that you can remove multiple files at once with the selection method.  

1. Locate and select the files you wish to remove.

2. Click the ... MORE button in the upper selection bar.

3. Click Remove in the drop down menu.

Further reading:
Admin Features