The Mojave installer doesn’t give you many options, but you can still approach the process in either of two ways:
Plan A: In-Place Upgrade: This easy, default method is appropriate for most people (including anyone Upgrading from the Mojave Beta), with some qualifications.
Plan B: Clean Install: Although the installer offers no built-in option to start fresh by erasing your disk, you can accomplish the same thing in a slightly roundabout way.
Most users should start with Plan A and then if (and only if) they encounter problems, move on to Plan B. A few people may want to skip Plan A and go directly to Plan B. In almost every case, the end result will be virtually identical, regardless of which path you take. ...