Download and save the firmware update for your device, and then double-click on the file to open it.

Check the battery for your Unifying device and recharge or replace it with a fresh battery, if needed.
NOTE: If you have Logitech SetPoint installed and running, click the SetPoint icon in the notification area, and then select Exit before you begin the firmware update process.

Launch the Unifying Software:
Start > Programs > Logitech > Unifying > Logitech Unifying Software

NOTE: If you don’t have Logitech Unifying software installed, you’ll need to download and install it first.

In the Welcome window, click Advanced.

In the left pane, select your device.

In the right pane, click Update Firmware.

Follow the on-screen instructions to finish installing the update. Check Firmware Version to confirm that the firmware has been updated.
Click Close to exit.

Once the firmware is updated, you can re-launch SetPoint:
Start > Programs > Logitech > Mouse and Keyboard > Mouse and Keyboard Settings