How can i upgrade soldiers using medal i dont get it

[weary oasis]

The purple medals are only needed to upgrade troops from level 8 to level 9. They are not needed to upgrade troops up to level 8. The cost to upgrade a troop to from level 8 to level 9, varies based on whether it's a Rare, Epic, or Legendary Troop. Here is the cost to upgrade:

In order to level up troops from 8 to 9, Purple Medals are required. These are primarily gained by opening the chests in Infinte Trial and both Challenge modes (Weather and Master). These are the hardest resources to get and build in the game, so leveling up troops to level 9 should be done sparingly. Notice, besides Purple Medals, you'll also need either Blue Gems or Gold. Here are the resources required to level up from 8 to 9:

Legendary:
Blue Gems = 2,944
Purple Medals = 2,400

Epic:
Blue Gems = 2,208
Purple Medals = 1,500

Rare:
Gold = 100,000
Purple Medals = 900

Common:
Never upgrade to level 9. These are only good for Fusion to get your daily quest reward