Just FYI, there are two sets of bathrooms at the Lava Pool. The ones under the slide the PP mentioned do have showers, but to be honest it’s a somewhat horrible, dark, damp place to change! The other bathroom is newer, clean, and bright - but doesn’t have showers so you’ll be changing in a stall. This is the one we use when we’ve needed to change in the past.
Same applies to the Oasis Pool - the bathroom there is newer and clean, but it’s just a bathroom as well.
Hope that helps!