Using your computer, click the download link in the email that's been sent to you after purchasing Cleartones. The files should now download to your computer's harddrive. Please note you cannot download the files to your phone directly, we'll use iTunes to synchronize copy them to your phone.
Open iTunes and connect your iPhone to your computer using a lightning cable. Tap "Trust" on your phone when it asks you "Trust This Computer?".
Click on the little iPhone glyph right under iTunes' volume control. This will
Select the tones you want to install on your phone and drag them from the finder directly on the "Tones" menu item in the sidebar. The tones will be copied and synchronized automatically, and should now show up in the ringtone picker on your phone. Go to Settings > Sound and Haptics > Ringtone and tap the name of the files to preview them.