If you would like to change your subscription from HiFi to Premium, or from Premium to HiFi, the process is the same.
Go to TIDAL.com - MENU - MANAGE ACCOUNT, and log in with either your email and password or the Social Media account that is registered with TIDAL.
Click on Subscription, then choose either Upgrade for HiFi or downgrade for Premium.
When you change your subscription from Premium or HiFi, the changes will take place immediately.
**Please Note: Your billing date will be changed, this is because 2 Premium days = 1 HiFi day. Thus the remaining days until your billing date will be cut in half.
When changing from HiFi to Premium, you will be downgraded at the end of the billing cycle.