update keeps timing out

Try this standalone "combo" update: Download macOS Mojave 10.14.6 Combo Update

If you can't even start your Mac because it's stuck attempting to finish the update, you can restore its previous system with Time Machine: Revert your Mac to a previous macOS version - Apple Support. Time Machine automatically creates a "local snapshot" of the previous system prior to installing updates. In Step 4 you will be selecting the Mac's own startup disk—the one named "Macintosh HD" unless you renamed it to something else. Restoring that system in that manner only a couple of minutes.

Do you mean that the download is timing out, this might be because you are using WiFi to download,

try using a cabled connection to your router.