Do I need to upgrade?
If you already have the latest firmware, you don't need to upgrade :)
USB2AX v3.2a and v3.2b shipped with firmware v04.
USB2AX v3.1a shipped with firmware v03.
Here is the latest firmware for the USB2AX. Righ click and “Save link as…” to download it.
v05 RC1 - 2017/07/27 - for USB2AX v3.1, v3.2a, v3.2b
For changes, see the changelog.
v03 - 2012/09/14 - for USB2AX v3.1 - initial release
Note: Firmwares for earlier versions of the hardware can be built from source (need to change the board type for LUFA in the ASF Wizard) or asked for by email at firstname.lastname@example.org.