Sharlene,
You don't need to inform the staff. On that day, just 1) give them your card so they can sign you in, 2) write in the list to rent their gym towel (small towel), 3) then can proceed to the changing room (depends on whether you decide to take up the aerobics or power package, there are different changing rooms). From there you can make use of any of the lockers.
They do have permanent lockers for us to rent, but I personally don't think it's necessary (plus if you're someone who likes to travel to different outlets, it wouldn't be feasible to rent). Most people prefer combination locks as there are no need for keys, but it's really up to you. I bought my lock at amore, but recently at Metro, they have funky colour locks selling for about $2, you can check those out.
Amore doesn't provide free usage bath towels, which I think is rather crap! Other clubs like CF, PF, Fitness First, they're all providing free usage. I mean, what's the big deal!?! Anyway, call me a scrooge, but if they wanna charge for bath towels, I'd rather lug my own!