Go to above link and select your phone model then download Developer ROM
After that you will get a zip file which you can save anywhere in your phone. After that backup all your important data.
Then Go to tools folder in your phone where you will find updater. Click it.
After that go to top left of updater upon clicking on dots you will get options as shown in image.
Choose update package and select the downloaded package zip file and continue and follow the instructions. You will get your latest MIUI version.