You can change your subscription by going to the subscription center in settings and selecting your new tier. 

For Mobile:

1. After logging in to your account, tap the menu (avatar) in the upper left corner of the screen
2. Tap "Settings"
3. Tap "My Subscription"
4. Choose the subscription tier and tap "Switch to this plan" under the applicable tier

For Web:

1. After logging in to your account, click on the menu (avatar) in the upper right corner of the screen
2. Click on "Profile & Settings"
3. Click on "My Subscription"
4. Choose the subscription tier, and click on "Switch to this plan" under the applicable tier