My dog has bumps on the belly

Hello

My dog Rizzo, a Golden Retriever with 13 years, has bumps on the belly. The a bump is the size of a pigeon egg, but flat. The new bump is only a third of them.

You have an idea of what it could be or it is dangerous? I can easily afford the vet and would ask for advice beforehand likes.

Am grateful for any hint.

Doris