How can I reset my family tree?

if you cant delete someone it is because a spouse is attached, you either need to delete the spouse or disconnect them. it is never worth deleting your whole tree and starting from scratch, everything is fixable

*or has children attached

Of course, if any profile on your tree is merged with someone else's profile, the tree is now a shared responsibility, and deleting may not be appropriate any longer.
If profiles are duplicated, it is usually better to merge them than to delete them; this insures that all pointers are preserved.