Using an iMac (27-inch, Late 2013) - Attempted to update to High Sierra earlier this year and the computer got stuck in "can't update... please retry" mode - I had to force it to shut down. I had to erase the computer completely, download the original OS, reinstall the OS ... THEN, update to Sierra... THEN, restore from backup. This took about 2 days. Everything was fine after the restore, but I never attempted to load High Sierra again. Can I update to Mojave from Sierra... and is it SAFE to try? I'm very reluctant, but want to have the latest OS.