I understand this isn't a Mojang problem, more a Microsoft problem, but I feel this information would still be useful to have. To upgrade from the old launcher, you open the old launcher and click "Download it now!". You then get brough to the web browser, which then takes you to the Microsoft store. The first option shown is then "Buy with Game Pass" and the second option is open xbox app. Then, you are brought to the Xbox App, where the first option is again "Buy with Game Pass for PC" and the second option is finally install for free.