First find the latest update file for your device in ReplicantImages, it will look like that:
replicant-6.0-<yourdevice>.zip
1. Download the update file on your computer
2. Make sure the device is started up and has an Android system running
3. Connect the USB cable to both the computer and the device
4. Enable USB mass storage on the device
5. Mount the mass storage on the computer
6. Copy the update file at the origin of the mass storage
7. Safely unmount the mass storage on the computer
8. Disable USB mass storage on the device
1. Press the power button
2. Select Reboot
3. Select Recovery
4. Press OK
1. Select Apply update
2. Select Choose from emulated
3. Select the update file, which looks like that: replicant-6.0-<yourdevice>.zip
Note: With Android 4.2 and later, it may be located in the 0 directory
4. Confirm the installation
5. Press the back key (if necessary) to get back to the general menu
6. Select Reboot system now to reboot the device
7. Your device should now be updated!