To delete an Activity Button that you created, simply press & hold (like you would do for an app on your iPhone). You should see a wiggly "X" icon appear. Tap the "X" to delete. Note: you cannot delete the default Owaves' Activity Buttons.
To re-order an Activity Button that you created, also requires a press & hold (like you would do for an app on your iPhone). Simply drag and drop the Button(s) to the new position you would like. Tap anywhere on the surrounding blank white space to de-select and undo the wiggle — which will set the new position of your Buttons.