My neighbors did that, ended up replacing a a beautiful patch of natives with a more formal manicured look. It was sad to see the change, but if they offered me some of them plants it would have made it slightly better.

Do it in fall.

Also consider carefully what's there. If there were ferns, it might be shady, so that will impact what can thrive there.

I agree with fall for planting shrubs, and next spring obviously for annuals. I also agree with the PP that lots of people will likely be happy to take your unwanted plants off your hands (as long as nothing is an invasive).

Fall is a good time to dig up those ferns etc and move them or give them away. (I would love to take your ferns!!!) And it’s the best time to plant shrubs. Plant the annuals in spring. This week is good gardening weather but extreme heat is just around the corner and that’s really hard on new plants.

But are you sure you can’t work with what you’ve got? It’s possible that with a little work you’d end up with something great.

You can do it right now. The weather isn’t hot but it’s been really dry so you’ll just have to make sure you keep new plantings well-watered.

We inherited a northeast flower/fern bed from previous home owner. While neighbors told us it was a fantastic spot once upon a time, it got left uncared for and then we spent a few years figuring what grows there. The result is that it looks beautiful for a hot second in spring and then looks overgrown and crazy. Come Fall, it all dries up.
We want to dig it all up and plant a few small evergreens and a tiny bit of annuals for color.
What is the best month to start this overhaul?