Hey guys I bought my new router asus rt ac66r and want to give me the link to the tutorial to install the asus-merlin from scratch bone I have the original asus firmeware to install the merlin
The short version is download the file, unzip and use the gui to upload the firmware you want to use.
After flashing the firmware you want, make sure you do a full reset to factory defaults and follow with a minimal and manual configuration to secure the router and connect it to your ISP.
The following links may also help you get the most from your network after flashing the latest firmware on it (and help you understand why the above link/steps are necessary too).