Need help with the recovery mode

Hi, I have an HTC one M7 Original Sense of AT & T, some time ago I decided to switch to Google Play Edition and everything was fine, I received all updates, etc ...... until now I want to root, but when I try to enter recovery mode fallen Android logo with a red triangle appears in the middle, I have no idea what I can do. Please I need help to repair the recovery mode and take root. Thank you.
PD: Please explain me as a beginner.