Mounts can be upgraded only when they’ve composed with a Mount Soul. Sapphire  is required to upgrade the mount. You can choose one of the initial attributes to enhance. You can enhance a single attribute nine times by using Sapphire. (The higher the attribute is, the lower the success rate is.) As the attribute gets higher , the success rate will be lower.

How to grow a mount
Put Mount into sun slot of Magic Cube, Sapphire into moon slot and corresponding ores into star slot —- Left for First Attribute, Down Left for Second Attribute and Up Right for Third Attribute —- one attribute at a time, and then click “Run”. If it fails, you’ll lose all the materials except for the Mount. If it succeeds, the chosen attribute will go up 1 level.

Ores: a level 5 Iron Ore for the first to ninth upgrade, a level 5 Silver Ore for the tenth to eighteenth upgrade and a level 5 Gold Ore for the nineteenth to twenty-seventh upgrade.

How to obtain Sapphires
You can buy Sapphires at Marsha’s (Genotian) and Manitor Messenger ’s (Natarian).