There are two ways you can upgrade a tablet to the latest Ocean Tablet app.
If you're only upgrading one or two tablets and the tablets are in front of you, tap the cog in the bottom left hand corner. Enter your Ocean user credentials and choose "Update Wave". The upgrade should only take a minute but you'll need to repeat it for all the tablets you want to upgrade.
If you're upgrading many tablets, it's easier to use the Ocean web portal to trigger the tablets to upgrade. Log into Ocean on your computer's web browser, go to the "Tablets" tab and find the tablet(s) you want to upgrade. You can click them and an option to upgrade them will appear. The next time those tablets are used, they will upgrade themselves.