Sitecore Uninstall

 1. Delete the Sitecore instance folder from C:\inetpub\wwwroot and Solr Folder.

2. Run PowerShell as Admin and use SC.exe delete <Service Name >

and delete Sitecore and Solr services .

3. Delete Sites from IIS 

4. Delete the database from SQL (Optional)

Done !!!

If you get any error deleting the root folder in step 1 then stop Sitecore services and stop sites from IIS.