Here are some of the items needed.
My post was rotten at the bottom.
You can start by removing hardware.
Once hardware is removed, remove post if it is broken or rotten.
You may need a pick to dig in hard soil and a sledge hammer to break the concrete. Remove soil and debris. Wear your safety glasses.
It may take some time to dig out the soil and old concrete.
Insert new post and ensure it is straight. Use the level.
Replace some dirt and compact. I used the old post to compact.
Mix the concrete. I used one 50lb bag because our soil is very hard and I used the old concrete for additional strength.
I mixed the concrete in a 5 gallon bucket. Pour into hole and wait. You may need to support the post with boards like in the previous photo. Let dry over night and fill with soil.
Remove latches or hinges from old post and place on new post. You are done.