I get the message that audacity needs to be updated. I just installed it. What do I do?

What do you mean what do you do?

Software packages are distrubuted by the developer. They create a change/update. You install the distributed package and then when told to do so you install the update to the package.

Right/control click on the icon and chose "Open" from the drop down menu.

Update it?

Make sure you have version 2.4.2.0.

What happens when you try?

You're welcome.