Found the answer...
It seems the description here is not right:
http://pocketbook-global.com/downloa...ade_manual.doc.
It should be:
. Copy the upgrade image (file named SWUPDATE.BIN) to the root of your memory card.
2. Insert the card into the cardreader of your device.
3. Connect your PocketBook 302 to power supply (to power outlet with the help of the wall charger or a computer with the help of USB-cable). The device has to be connected to power supply during the whole process of the upgrade.
4. Turn the device off.
5. Holding both Big side buttons (page Up) simultaneously, press the “On/Off” button as if you were turing the device on. IMPORTANT: both “OK” and Upper Page buttons must be released ONLY after the message «Firmware update» appears on the top of the display (after the logo appears and dissapears! - don't release buttons after the logo appears - wait untill it goes away and you see «Firmware update» words!)
6. The programm will check the upgrade file image. In case it is succesfull, the display will show «Press center key to start update».
7. Press the center “OK” key. The upgade process takes about 2 minutes. After it is finished, the display will show the following message «Upgrade OK. Now please reset the device».
8. You don’t have to manually reset your Pocketbook 302, as it resets automatically.
9. Turn the device on. Make sure that the latest firmware on your PocketBook 302 is installed. To check this, please go to Settings - Information about device - Firmware Version.
Found it here:
https://www.mobileread.com/forums/showthread.php?t=75411