Mac OS update

macOS upgrades do not happen automatically. They must be manually initiated.

Not sure where you downloaded the Mojave dmg, but it may only be the updater for an existing installation.

Delete that installer and follow the guidance below.

❗️ Do NOT upgrade until you have made a Time Machine or other backup of your startup drive.

Learn How to Back up your Mac with Time Machine

How to Upgrade  macOS:

The macOS version you can upgrade to depends on the year your Mac was released.

Click the  (Apple) menu at the top of your screen and choose About This Mac.

Check the Compatibility of your Mac with newer versions of macOS:

➡️ macOS 10.14 Mojave is compatible with the Macs listed here

✅ - IF your Mac and apps are compatible, then using Safari only, download the macOS upgrade installer app:

Click >  Mojave, 

Once downloaded, double-click the “Install macOS…” app in the Applications folder to begin the upgrade.

Please see > How to download macOS.

Back up your data, check the application compatibility table, click here, and then on the download link for Mojave. The dmg you found is an updater and can't be used for a full-version upgrade.

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Yes. There absolutely is a chance of losing all of your data should the upgrade not go smoothly.

Moving up to Mojave may require your Mac to make certain changes to the disk drive formatting and the potential for trouble is not zero.

There's a possibility at any time due to drive failures or other causes.

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