I'm preparing to hang a ceiling fan fixture in a bedroom. I need to remove an old ceiling light's electrical box and brace first, however I don't see how I can remove them. The brace has limbs which sit underneath the joists and above the ceiling plaster and it feels like they might be screwed into the joists. There is a bit of lateral wobble to it so I don't want to reuse it for the fan fixture. (also because it'd be attached on the underside of the joists)
Here are some pictures: https://i.stack.imgur.com/QzHZe.jpg
How do I remove it? Or should I secure it somehow and reuse it for the fan? The fan fixture is 26 lbs. My house was built in 1946 and I suspect the brace is original.
[update] I was able to use the RozoZip, though I wasn't able to get as close to the joists as I would have liked. But after widening the hole with a file I installed the new box and brace.