Delta Drive, Delta Trust & My Drive · Using Delta Drive
Why can't I delete the Shared, Team or Documents folder in Delta Drive?
Short answer: The five starting folders can't be removed because backups and shares point at them, but their contents can. Right-click one and choose Empty this folder… to move everything inside to the trash.
Those five starting folders are what your backups and your shares point at, so removing one would break them. Everything inside them is yours to delete like anything else.
To clear one out quickly, right-click it and choose Empty this folder… — its contents go to the trash and the folder stays where it is.