Imovie will not update

Try rebooting your computer. Then again attempt the download.

Also, you might let the download keep loading overnight to see if it will complete.

You could also try booting up in Safe Mode and, after everything loads, immediately shut down and reboot in normal mode. Then see if iMovie will update. Here's a link that shows how to boot up in Safe Mode:

Start up your Mac in safe mode - Apple Support

If still no luck, try the following:

Resetting the System Management Controller

Try resetting the System Management Controller (but no longer available for the new M1 computers):

Reset the SMC of your Mac - Apple Support

Resetting the NVRAM or PRAM

Try resetting the NVRAM or PRAM.

Reset NVRAM on your Mac - Apple Support

Contact Apple Support

If none of the above resolve your issue, contact Apple Support.  The techs there have the capability of remotely accessing your computer that we cannot do here.  To contact apple support click on the Get Support item in the upper right hand corner of this forum’s screen.  Navigate to a place where you can enter your phone number.

-- Rich

iMovie 10.3.4 cannot not be updated because it already is the current latest version. I assume that you meant you were trying to update from an earlier iMovie version to 10.3.4.

iMovie version 10.3.4 requires 3.5 GB available disk space, so confirm that you have at least that amount of space on your drive. You should have at least 10 GB more than that to ensure that iMovie has sufficient application space to operate efficiently.

If the above is not applicable to your situation, try using the procedure below to do the redownload:

To update/redownload iMovie 10, drag your iMovie 10 app from the Applications folder into the trash, but do not empty the trash. Sign in to the app store and open your purchases folder (account folder) by clicking on your name at the bottom of

the app store side bar. You will see your purchases displayed, including iMovie 10. Redownload/update iMovie from there. If not successful, drag your present iMovie app out of the trash (if you moved it there) and return it to the Applications folder.

-- Rich