You can edit the buttons that appear in different locations inside AltaMail, such as the side menu panel, the popup panels menu (View) or swipe settings (View). Open each settings (View) screen and you will see a list of buttons.
Tap twice on the trash can icon beside the button to remove it.
Tap and hold on the 3 lined button on the right to drag and rearrange the list order.

Tap on "Add" at the top of screen to choose some more buttons. Tap to select the new buttons and then go back to the first settings screen and the new buttons will be added at the bottom.
When you are adding new buttons, you can tap on the settings cog button beside each group name to edit the group list. eg. add new folder filters (View). You can also use the "Choose" button beside the email folder group name to choose any email folder you want.

If the "Default" button is visible, tapping this will change all the buttons to the default list.