Trouble Importing please help

I’m trying to import an eXtended RSS (WXR) file with all my posts, pages, comments, custom fields, and categories from another site I have.

However I keep getting errors that say the files already exist despite me having gone and deleted everything. I also get this error…

Option Tree “Media” already exists

Is there any easy way for me to delete everything within this wordpress site or set the import files to overwrite the older files?

Thank you!