I have not been able to update my Macbook for the last 7 mo. I am currently using mojave

What update are you trying to install, is it an update for Mojave or are you wanting to upgrade to Catalina.

These are the most recent updates for Mojave,

https://support.apple.com/kb/DL2010?viewlocale=en_US&locale=en_US

https://support.apple.com/kb/DL2045?viewlocale=en_US&locale=en_US

Once downloaded double-click to install.

If you want to upgrade to Catalina,

Open Safari do not use Firefox and click on the link below,

How to upgrade to macOS Catalina – Apple Support

Go to Section 4 and click on Get macOS Catalina

you will be redirected to the App Store Catalina download page.

It should say Get or Download.

Before upgrading make a full back up of your Mac.

Check that third party apps you use have updates available for the new OS.

https://roaringapps.com

Check that your printers/ scanners etc have updated drivers and software available for the new OS.

Connect your mac to your router via cable rather than rely on WiFi.

Do not use your mac while it is downloading

and do not use any other devices that share the same internet connection.

If the App Store says ‘Open’ then it is detecting a previous download of the install app

go to the Applications folder locate Install macOS Catalina.app.

Move it to the Trash, empty the Trash.

Restart, click on the link again, the App Store should say ‘Get' or 'Download'.

If you are considering upgrading to Catalina be warned that it does not support 32bit apps.

Your Mac is probably running 32bit apps and these will need to be updated to 64bit apps,

some updates may be free, some may be paid. Use this app to discover which apps you have

are 32bit, https://www.stclairsoft.com/Go64/. Once the list has been created you can then

contact the developers of the apps to see if they provide 64bit updates.