Delete profiles is only possible if they are not used by any series. From the main sonarr page (list of series), you can see which profile is assigned to which series.
To easily change profiles in bulk: go to the Series Editor (button on top), then sort by profile. Select series as desired, select the desired profile at the bottom and hit Save.
Once a profile is no longer in use by any series, the delete button will be available.
Quality: create or edit a profile where the lowest quality you want is also the cutoff quality. Picture + info here.
In your example above, for the “Any” profile, set the cutoff to SDTV. Whichever is available first (SDTV, WEBDL-480p or WEBDL-720p) will be downloaded, and sonarr will stop upgrading the quality, because it meets or exceeds the cutoff quality.
Do you mean you see multiple files for the same episode, in different qualities? That should not happen. When sonarr upgrades the quality, it deletes (or should delete) the lower quality file as part of the upgrade process.