In general, you normally cannot "Delete" sources from the database. You can only detach them from records that they are attached to.
Go to the person's source list, and select the title of the source. When it opens there will be a detach button. When you detach the source, all tags to other vitals that it had will be removed as well. However, any values for vitals or other information that was derived from that source and recorded in the person record will have to be manually removed.