I'm sure it's been answered already, but I can't find it. Once a set of pictures has been posted in the gallery, can you add or remove pictures, or do you have to create a new gallery?

We've made some big changes to our theater over the last 2 weeks, and I wanted to post some updated pictures this weekend.
2 M80s, 1 VP180, 4 QS8s, 2 EP800s, 4 M3 Outdoor, 2 M3 Rosewood, 2 M5HPs Rosewood, 1 AxiomAir