...got a message that there is a compulsory upgrade.
Could you please tell us where this message was sent and where it came from?
Sometimes it is not the downloading of the app which is problematic itself. One may download the legit app but still fails to protect his/her BTC due to messages such as the one you received giving fake instructions.
How sad, another scam victim using Bitcoin. I don't know if this is probably the result of naive people using Bitcoin without enough technical knowledge on how to use it. Sad to say that probably 25% belongs to this kind of people that we called prey from scammers. If they are educated very well they won't fall into this kind of scammers trap.
25% is too low in my opinion. I guess more than 70% of BTC owners have made a misstep or two along the way that could have totally wiped out everything they own. It so happened that scammers are eyeing the significant amounts.
When I finally got into Bitcoin myself several years ago, I was quite enamored by the revolutionary philosophy behind it and I was too excited to own a little amount just to share with the feeling of being part of the entire saga. But that was before I got educated by the technical aspects of its security. I think this is also happening to many other newcomers probably including the OP.