Install Mojave
I have an iMac C1***NCR running macOS High Sierra 10.13.6. It is running incredibly slowly, taking at least a minute or two to open up any App (e.g. Word) or even to open a document when Word is already open. The hard drive has only used about 10% of its capacity, so it is not overloaded. I thought that perhaps I should instal Mojave, but when I click on Open on the Mojave installation site it tells me that it is "damaged" and can't be run. Any suggestions on what I should do please?
[Edited by Moderator]
iMac 21.5″, macOS 10.13