It's easy!
Tap on the asset you want to stop following to open it
Tap on the star in the top right to stop following (it will go from golden to an outline of a star)
If you are following multiple pairs for a cryptocurrency, "un-starring" the coin will remove all followed pairs from the list. If you wish to only unfollow particular pairs, see the steps below:
Open the followed asset from the Following screen or by clicking here.
Tap on the price source (exchange and pair) above the price chart.
Un-star or star-specific pairs that you wish to unfollow or follow, respectively.
PRO TIP: Unfollowing a coin is different than unfollowing a coin on Delta Direct. You can unfollow a coin on Delta Direct by scrolling down the page to Direct and toggling off "Notify me for each new XXX Direct".
PRO TIP 2: To follow a coin, you can follow this guide here.