To install a custom recovery on your OnePlus One you’ll first need to unlock the bootloader on your phone, here’s the guide to do so.
In case you already have a unlocked bootloader, please take a minute to go over the cautionary notes before you proceed:
Next, download the TWRP custom recovery:
Download the latest build, rename it to recovery.img. It is imperative that you rename it to nothing else but recovery.img. Place the renamed file in the platform-tools folder of ADB you’ve setup. If you haven’t setup ADB then do it now.
Turn off your phone and boot into fastboot mode: hold volume UP & power together until you see the display say fastboot mode.
Navigate to the platform-tools folder inside ADB and issue the following:
One the process completes, disconnect your phone from the computer and hold the power button to turn it off. To enter the custom recovery hold down the volume DOWN & power buttons.
You should now be greeted by the TWRP custom recovery screen.