If you don't already know, llantita is the diminutive form of llanta, which means tire. On it's own, it could be interpreted as a "little tire", but that's not the case in this context, so let's take a look at things and figure this out.
Quitarse means "to take off", and is a quite a useful verb, but maybe we'll discuss quitarse at a later time in more detail.
Llantita is a colloquial way of refering to what we like to call a "spare tire", and not the kind you keep in the trunk of your car. Yes, I'm refering to the ever annoying roll of fat that lives around our waist and can be nearly impossible to get rid of.
Now we're ready to make our translation...
Quiero quitarme la llantita
I want to get rid of my spare tire
You could also refer to your spare tire as a "llanta", or "michelines".
Another way to talk to about losing your spare tire is to use the verbs eliminar or bajar.
Pan comido, right?
I'm sure none of us like talking about our spare tires, but if you have to, you can now talk about them in Spanish!