How do I power up a PokéStop or Gym?
You and other Trainers can temporarily power up PokéStops or Gyms by uploading AR Scans of the location.
When you visit a PokéStop or Gym, you may notice a ring around the outside of the Photo Disc. This ring is an indicator of the level to which that PokéStop or Gym has been powered up. Each PokéStop or Gym can be powered up to levels 1, 2, or 3, with each subsequent level providing more powerful or valuable items. PokéStops powered up to higher levels will also sustain these benefits longer.
To power up a PokéStop or Gym, you must contribute location points, which are represented by tick marks around the outside of the Photo Disc. Contribute location points to a PokéStop or Gym by uploading an AR scan of that location, more AR scans will contribute more location points and power up the PokéStop or Gym to subsequent levels.
Note: Powering up PokéStops and Gyms is currently only available to Trainers in certain regions as part of a test. The final functionality is subject to change. We look forward to sharing this feature with more Trainers in the future.
How to Power up a PokéStop or Gym
Once you are within range of an eligible PokéStop or Gym, you can follow these steps to power it up:
Tap on the PokéStop or Gym to view the Photo Disc.
Tap on the power up button in the bottom right
Tap Scan PokéStop or Scan Gym
If this is your first time scanning, you will first need to review the safety information and tap OK
Take a scan of the PokéStop or Gym. For instructions and guidance on how to take an AR scan, see this article.
Tap Upload now to contribute to that PokéStop or Gym immediately, or Upload later to save your scan to submit later. Please note that if you choose to upload later, you will not be able to contribute location points until the scan has been uploaded successfully.
Once a PokéStop or Gym has been powered up to a new level, it will change its appearance on the map. This will let you and Trainers easily see that it has been powered up and can move there to benefit from the additional bonuses.
Note: Not all PokéStops and Gyms are eligible to be powered up. Ineligible PokéStops and Gyms will not feature the power up button on the Photo Disc view.
Source: Official Pokémon GO site