Dividers split a room into multiple regions for takeoff purposes. This article explains how to remove a single divider so the adjacent regions merge back into one.
1) Open the Divider menu. On the Takeoff ribbon, in the Room group, click the dropdown arrow below to Divider.
2) Click Delete Divider from the dropdown menu (Image 1, marker 2).
3) Hover over the divider you want to remove. MeasureSquare will highlight (in green) the divider line in the room:

"Remove a region divider. The last region can not be deleted. Right click to cancel and return to ready. – Aligning on 1/2" (Image 2)
4) Click the Divider to confirm. The two regions on either side will merge into a single region, and the updated dimensions will display on the plan (Image 3 — the Reception area is now one region measuring 12'0" x 16'4").