How do you upgrade from High Sierra to Mojave?

Thanks! I was able to find a copy in my application file and was able to throw it away. However, when I click on the download button it gives me a message that it is calculating but then it goes out to lunch per se and does not finish. Any ideas?

I tried to download Mojave and I get a message that the copy of the install is damaged. Do you know what I should do?

The Mojave download never did work for me but I was able to jump up to Catalina. It took awhile. Maybe need to upgrade my internet. All good now. Thanks!