Through Fastboot

1) Download the latest recovery file

2) Rename your TWRP file to twrp.img and transfer it to your platformtools folder

3) Boot your device to fastboot and plug it in to your PC

4) Open a terminal in your platformtools folder

5) Type the following in your terminal and then hit enter:

fastboot boot twrp.img

6) Once booted, go to Advanced > Flash Current TWRP

Upgrading to a Newer Build

1) Download the new TWRP build to your internal storage

2) Boot to your current TWRP

3) Go to Advanced > Install Recovery Ramdisk

4) Select the new TWRP image and Swipe to Install