How to completely change body?

When I first signed up, I chose to be this furry thing (Luskwood Ringtail Shape Male). I'd rather go back and start with another choice. I can't figure out how to do this, though. There doesn't seem to be an option to ditch the head and the tail. How do I start over with another template?

There should be some set avatars in your Library.

First right click and detach all items, and detach all clothing (don't do it in a PG sim!).

This way, if you don't know what's going on, it will set you as blank.

Look in your library and on a folder of a regular "Male" or "Female" right click the folder and select 'add to outfit'.

This should replace everything you are in and set you to a normal human appearance.

as seola said, all the choices presented when signing up, are in your 'library' so you can feel free to explore a lil an try on any of them you would like, it will copy them from the 'library' to your main inventory each time, so you can also edit/modify them some and later get the originals again fairly easily

Your body consists of several parts: Shape, Skin, Eyes, Hair.

Shape is your body shape.
Skin is the texture that goes over it.
Eyes are what they sound like.
Hair... more on this in a moment

To "change" a body part, find the part you want to change to and "Wear" it. Either right click and select "wear", or drag it onto your body. Give SL a chance to rez the new part.

What has already been posted is valid... those are complete bodies as part of an outfit. But, you are not restricted to that. You can buy new body parts, or make your own. To make your own, go into "Appearance" mode and select "new". Play with the sliders till you are happy. You can directly edit the number to fine tune the body.

You cannot "take off" a body part. It will always be "worn" until you replace it with a different part of the same type (ie: a skin can only replace a skin).

Hair. The hair you started SL with is a body part. However, what you see on many people in SL are prim hair attachment/s. underneath, we've replaced our starter hair with a bald hair (or colored) base. Like with other body parts, the bases can only be replaced... not removed.

You indicated that you wanted to start over with your body, so I would recommend first removing all the Luskwood attachments. Then with the remaining shape and skin, either do what the other posters recommended, or go into appearance and create a new shape/skin/eyes and/or a hair. Very Important... if you create a new body, save it.
And, make a copy of it. You can then always revert to the copy as a backup if you accidently damage your original (we've all done it... tweaking our shapes beyond the point of repair).