Prune it hard in early spring.

I would whack it to a foot but you could leave half the stems longer to the lowest green growth if whacking that harshly scares you.

Thanks, I don't care if I get little bloom next year as long as I don't kill it. should I wait for some green or prune it dormant?

Wait for some green. The safest course would be to cut half to the lowest two green buds and the other half almost to the ground.

If you cut the entire thing below green buds, it may kill it. I have not killed any doing this but I've read posts from those who have.