How can i upgrade notes app later. I didn't updated at first time. Ipad mini
iPad Mini, iOS 9.0.2
Once you're ready to upgrade, open Notes and select "Upgrade".
Upgrade your notes with iOS 9 and OS X El Capitan - Apple Support
Be aware that you must be using/syncing iCloud Notes from your main Apple ID to upgrade Notes. If you are using multiple notes from multiple sources (Gmail, Yahoo, another different Apple ID, etc), you may not be using/syncing your main iCloud Notes (I was not) so be sure this is enabled under:
Settings/iCloud...be sure Notes is turned ON here.
Run the Notes app
Tap the < arrow until you reach the "Folders" pane on the left side
An "iCloud" heading should be shown at the top with an "Upgrade" button
Tap the "Upgrade" button to perform the upgrade
How can i upgrade notes later. Ipad mini
