Open the .dmg file and drag Oknola into Applications.
The first time you open Oknola, macOS blocks it. Open System Settings > Privacy & Security, find the message about Oknola, and choose "Open Anyway". Confirm with your password or Touch ID.
Before updating, open Settings > Account. Wait until it says Synced. If an upload warning is showing, wait for it to clear too. Let any import or image add finish.
Quit Oknola. Drag the new version into Applications and choose Replace.
Install and update on Mac
How to install Oknola on a Mac and update it without losing changes.