Selecting the option to Ungroup lists will remove the list group. You can then choose to Rename group or Ungroup lists.

On Windows or web right-click the list group to make changes to your list group. On mobile, tap the three dots to the right of the group name. On mobile you can also tap the three dots to the right of the group name and then select the option to Add/Remove Lists. To add lists to a group, click or tap and hold the list to drag and drop it in to the group. To rename it, just tap or click to select “Untitled group” and begin typing the new group name. This will create a group with the name “Untitled group”. With our latest update, you can create list groups to organize your lists. Just tap or click the list group icon to the right of +New List to create a new list group. To choose the background for a list, select the three dots in the top right and then select the desired color or image. Based on customer feedback, we've also reduced list headers to put the focus back on your lists and tasks. Customize each list with your choice of solid colors or full screen images – including the iconic Berlin tower from Wunderlist. We've given To Do a fresh new look with more background options.

Wunderlist vs microsoft to do