That's becuase you are trying to install the theme and there is already another version of it installed, you will need to:
- Delete the current theme version from WordPress Dashboard.
- Delete the current theme version using any FTP client from this directory (/wp-content/themes).
- Rename the old theme folder with any other name like “theme-old” for example.
Note: Don't worry to delete the theme files, you will not lose any of settings in TiePanel, as all these settings data are stored in the database no in files. However, any edits to the direct PHP theme files will not be kept after deleting the theme files, so make sure to have a back-up of these edited files.