First find out what 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. Connect the microSD card to the computer (e.g. using an USB card reader)
3. Mount the microSD card on the computer
4. Copy the update file at the origin of the microSD card
5. Safely unmount the microSD card on the computer
6. Disconnect the microSD card from the computer
7. Insert the microSD card in the device (make sure it is turned off before inserting the card)
1. Press the power button
2. Select Reboot
3. Select Recovery
4. Press OK
1. Select Apply update
2. Select Choose from sdcard1
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!