Watching neighbor’s turtles - should I clean the tank?

Hello turtle people on Reddit. I’m looking for some advice for my neighbor who asked me to watch his turtles for the upcoming month. Attached are a few pictures. He told me that I needed to feed them and add water to their tanks, but after looking online a little bit, it seems like they need a bit more. I’d like to at least deep clean their tanks, as I think the neighbor wouldn’t mind the help, but I am afraid that if this doesn’t happen often for the turtles, it could stress them or I could do it incorrectly. Could someone walk me through the basic process of responsibly cleaning a turtle tank? Thanks in advance.