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.
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M100x2,VP180HP,QS10HPx2,QS8x2,EP800x2,M3x4,M3x2 (Wood),M5HPx2 (Wood),AxiomAir,ADA1500-3,ADA1500-4