how do i stop update pop up when i open RB ?

If you're on a Mac, open the rekordbox folder, right-click on the app, select Show Contents, in the Contents folder open the MacOS folder, scroll to the bottom and rename the Upmgr rekordbox.app application to whatever you want, and it won't bug you again for that version.

On Windows, same thing, but you should find that within the rekordbox application folder.