Inside your Explorer Window, click on Workspace (this will highlight it blue).
Click the small grey arrow right next to Workspace. The arrow looks like this “>” and when you select it, the arrow will point downward.
Select the Baseplate once.
Press Backspace on your keyboard to delete the Baseplate.
Troubleshooting: If you click the Baseplate more than once, Roblox Studio tries to rename it. If you are having this issue, click on something else to un-highlight the Baseplate and try clicking it again then pressing backspace.