Sorry, but Apple does not permit that. If your network connection is unreliable, then try downloading from a different location. You will need to use a fast connection, preferably Ethernet rather than Wi-Fi. You are currently running Mojave, therefore, you will be upgrading to Catalina. I suggest you repair the drive and upgrade. How to upgrade to macOS Catalina.
Repair the Drive for El Capitan or Later
- Restart the computer. Immediately, at or before the chime, hold down the Command and R keys until the Apple logo and progress bar appear. Wait until the Utility Menu appears.
- Select Disk Utility and press the Continue button.
- Then select the indented (usually, Macintosh HD) volume entry from the side list.
- Click on the First Aid button in the toolbar and wait for the Done button to activate. Click on it, then quit Disk Utility.
- Select Restart from the Apple menu.
Also, see the following:
Before You Upgrade macOS
- Fix any problems before upgrading.
- Run First Aid in Disk Utility while booted from your Recovery HD.
- Backup. Make a bootable clone using CarbonCopy Cloner or use TimeMachine.
- Be sure your startup disk has 18-20GB of free space during the installation.
- Upgrade third-party software for compatibility. See App Compatibility Table - RoaringApps. If you have mission critical software, then DO NOT upgrade until you know that software is compatible with the version of macOS you are about to install.
- Disconnect all third-party peripherals.
- Download the installer which will be in the Applications folder. Quit the installer after it opens, then make a copy of the installer and save it in the Downloads folder. The one in the Applications folder will be deleted after a successful installation.
- The download is large, anywhere between 5 and 9GBs. It takes time to complete. Be patient.
- Double-click on the installer in the Applications folder. Click on the start button to begin the installation.