Options/ then just type "service books" without the quotes.
On OS6, it shows up right away as the 1st thing in the list. The OS may have that unfinished feeling to you, but only because you're not that familiar with it. There are issues with the OS, but the feature you want is very "finished". You just need to familiarize yourself with OS6. It is very different from all previous OS's.
If you aren't sure how to delete the service books, or which ones to delete, you shouldn't really mess around with it. It can cause other issues if you delete the wrong service books...then you're headed for more doodoo...
@ Midnight Draven - he's right....you're talking about previous OS's, not OS6. There's no "advanced" feature in the options list in OS6. Typing "advanced" in the options list yields no results.