How do I update Di2 firmware?
Modern Di2 bikes come with wireless functionality built into the rear derailleur. 12-speed Dura-Ace, Ultegra, and 105 bikes all feature wireless connectivity.
Updating firmware is relatively easy, you simply use the E-Tube Cyclist mobile app.
The tough part is updating the hydraulic (wireless) shift levers. Updating them is not straightforward, so here is a guide on updating wireless shift levers.
While you could previously also use the battery charger to connect your bike to a Windows computer, 12-speed systems only work with the SM-PCE02 tool and E-Tube Project V5 / Professional
If you're on 11-speed Di2, your bike doesn't come with wireless functionality by default. Therefore, most 11-speed users update and tweak their bikes using the E-Tube Project Windows software.
You will need the Shimano e-tube project software to upgrade firmware. Keep an eye on their firmware update page and whenever they release new firmware for your components simply connect your bike to a windows computer and run the e-tube project to start updating.
If you're using the SM-BCR2 internal battery charger to connect to your bike, use E-Tube Project 3.4.5 (or 4.0.4). Those can be found on the E-Tube Project Archive page.