Defunct entries in /wp-admin/options.php

Some of my sites are built using clones of my previous sites. Looking in /wp-admin/options.php I’ve just discovered several stale entries for long deleted themes and plugins.

Most of this is unimportant, but there are also text entries with urls, so the sensible thing seems to be to clean this file out.

How do I go about removing items that are included?

Are there any precautions I need to be aware of, besides the obvious back up before editing golden rule?