Upgrading your Experts increases their knowledge, making them better at answering questions. To upgrade an Expert, you will need to collect a certain number of their Expert card that you receive from the Mystery Boxes you open.
For each upgrade, you'll need a specified number of Expert cards depending on the level of your Expert. Once you have enough, you can go to the Experts tab, and tap on them. To perform the upgrade, you will need to spend the duplicate cards, as well as some Coins.
Tip 1: You can see how much your Expert stats will grow based on the white stars beside each category
Tip 2: Curious about how smart an Expert can become? The dark stars beside each category represents how good the Expert will be when fully upgraded!