Custom ROMs are the way to go for power users of Android devices. Some of the omni-present features are faster updates, better modifications, root access, custom recovery, zip aligned APKs, deodexed ROMs, more features, ports from other devices and whatnot. There is a class of firmware that hail from the Android Open Source Project, or AOSP. These ROMs are decidedly different from others, in their minimalist native feature set and more freedom towards change.
CyanogenMod has always been one of the most famous and trusted custom ROMs for Android devices. It was the first ever custom firmware for any device. The CM device database has expanded exponentially since then, and maintainers for every new device spring to action almost immediately. HTC One, being the latest and the greatest from the Taiwanese manufacturer has quickly joined the CM bandwagon, and you can install Android 4.2.2-based CyanogenMod 10.1 to your HTC One with relative ease.
Please not that this method has been tried and tested for years and known to be safe, you follow these instructions at your own risk.
Rooted HTC One with unlocked bootloader.
ClockworkMod Recovery on HTC One flashed.
HTC USB driver for One configured on your machine
At least 50% or more battery remaining on the device
Backup your data completely in a safe place.
Download the CM 10.1 Nightly for HTC One from get.cm/?device=m7 and the latest Google Apps package from goo.im/gapps, and transfer them to the root of your HTC One’s internal storage.
Boot your HTC One into recovery mode by pressing Power and Volume Down buttons simultaneously.
In CWM recovery, select Install ZIP from SD card, followed by choose ZIP from SD card, and flash the CM10.1 ZIP package.
Repeat the above step and flash the Google Apps ZIP file.
After having flashed both packages, select wipe data/factory reset in recovery.
Reboot the device.
You’re now running the latest available nightly for CyanogenMod 10.1 on your HTC One.