The classic Google Universal Analytics properties will retire soon. Google Analytics 4 is replacing Universal Analytics. You can now set up and switch over to the new Google Analytics 4 property.
If you have upgraded to the latest GA4, you can follow these steps to remove the old UA properties.
Important:
Your property, and all the reporting views in the property, will be permanently deleted 35 days after being moved to the Trash Can. Once deleted, the property is gone, and we are not able to retrieve any historical data or reinstate your reports.
Sign in to Google Analytics from a web browser on your computer. Then click Admin (gear icon at the bottom of the left navigation panel). Navigate to the Universal Analytics property you want to delete. In the PROPERTY column, click Property Settings. Once the Property Settings page opens. Click Move to Trash Can button at the top right corner of the page.

You will then see the confirmation screen, click Move property to Trash button to confirm and delete an Analytics property.