Please follow the update instruction carefully.

Update instructions from version 7.3 to 7.4 -

If your application has been customized, Then keep your file backup and follow the step-by-step instructions below-
1. Login to the Superadmin panel and go to System Settings. You will get a field of product update. Upload the update_7.4.zip file here.
2. Wait for the update to complete. If you see a white screen, don't be panicked. Clear your browser cache to see correctly.
Window: Ctrl + Shift + R
Mac: Command + Shift + R
If you face any kind of difficulties, let us know through tickets.
That's it.