If you have upgraded using the two trim button method, your bootloader itself is not upgraded yet. If your want to keep that one up to date, you just need to "activate" it. It is already on your transmitter.

Go to your Home screen,and long press "ENTER" to get into the radio setup menu.

 

Press "Page" until you are at the SDCard page

Scroll down to the "FIRMWARES" folder, and select it to access it

Select the firmware which contains the bootloader you want to activate (you can use a bootloader from OpenTX 2.0 and still have the OpenTX 2.1 as firmware. It are two seperate things) and click "ENTER"

when it asks you to flash the bootloader, press "ENTER".

Have fun and 

Just Fly!