To edit a regular investment, select 'investing' and then 'Regular investments' from your app's 'More' menu, and select the pencil icon on the investment you want to edit. From there you can change the amount you invest in it each month.
Cancelling a regular investment can be done from the same place. Just tap the bin icon on the investment you want to delete and we'll get this removed from your instruction.
You'll need to edit or delete your investment before 12pm the day before your next regular dealing day to allow enough time for your updates to take effect.