If you are comfortable with flashing with your smartphones you can proceed with the below given tutorial. Be sure to backup your data and files before flashing your smartphone because Oxygen OS will wipe out your entire system data as well as files.

So all you need to do is download the Oxygen OS ROM from here and flash the OnePlus One smartphone with the latest ROM. Following are the step-by-step guide to achieve the needful.

The following instructions assume you have Fastboot and ADB installed.

Step 1

• You need to flash a system recovery onto your device. OnePlus recommends using TWRP for the process. Please download the recovery image to your computer.
• Boot your phone into fastboot mode by holding down the power button and the volume up button together. When you see the fastboot logo, connect your device to your computer.
• In your computer terminal window, locate the folder where you put the recovery image and run the following commands:
• fastboot oem unlock (You can skip this step if your phone’s bootloader is already unlocked).
• fastboot flash recovery . Image file should be the TWRP recovery image.
• fastboot reboot

You should now have the recovery installed.

Step 2
Unzip oxygenos_1.0.0.zip file you’ve just downloaded. In the uncompressed file you will see a oxygenos_1.0.0.flashable.zip file. Copy oxygenos_1.0.0.flashable.zip to your phone. If you’re using a Mac system, you can use Android File Transfer to solve the purpose.

Step 3
Boot into recovery mode again. You can do this on your OnePlus One phone by holding down both the volume down key and the power button together.

Step 4
Once you are in the recovery interface, factory reset (systemp wipe) your OnePlus One smartphone.

Step 5
After the wipe, locate the oxygenos_1.0.0.flashable.zip and install. Confirm flash. This command will successfully flash OxygenOS onto your device.

Step 6

• After the flash succeeds, you can reboot the device, which will take you to the new OxygenOS.
• Download and Install the Oxygen Feedback App.
• Download the apk installer file from here.
• Enable the installation from unknown sources from settings->security on your OnePlus phone.

Note- If you feel to rollback to CM, Make sure you have TWRP or CM recovery on the device. Another factory reset will be needed before flashing unfortunately so make sure you backup all of you data before commencing. Flashing OnePlus One does not void your warranty.

Accroding to OnePlus, following are the few known issues of the latest build-

• When printing images, printer service may stop.
• Cannot hang up a call using headphone controls (intermittent).
• OTG can only recognize FAT32 file system.
• During system update, display of wifi/data notification may be incorrect.
• During system update, display of version number may be incorrect.
• Files sometimes crash when uploading files to the cloud.
• Files may crash when renaming image files.
• Files does not support multi-select deletes.