WordPress is not fully deleting themes making themes to merge

I have a new WordPress website https://www.presipicedecisiontrainingacademy.com It is under construction. but I cannot get any theme to work properly. I tried deleting all installed themes but was unsuccessful. Some themes refused to delete at all while some have partially deleted. I am currently unable to move forward with the site setup. Everything is all messed up.
How can I delete all the themes and start from scratch? Clicking on delete at the bottom of the page I select the details or customize page is not working. Instead, several themes are all now merged