this may be stupid question, but I could not find direct solution to this. I often want to unsplit window as follows

+--------------+-------------+             +--------------+-------------+
|              |             |             |              |             |
|              |             |             |              |             |
|              |             |             |              |             |
+--------------+             |     -->     |              |             |
|              |             |             |              |             |
|              |             |             |              |             |
|              |             |             |              |             |
+--------------+-------------+             +--------------+-------------+



+--------------+--------------+            +-----------------------------+
|              |              |            |                             |
|              |              |            |                             |
|              |              |            |                             |
+--------------+--------------+    -->     +-----------------------------+
|                             |            |                             |
|                             |            |                             |
|                             |            |                             |
+-----------------------------+            +-----------------------------+

currently, I start with ctrl-x 1 and then split vertically/horizontally. but my real qustion is how can one remove a particular window split with out disturbing the other window structure.? is there any elisp function in built.?

hope I frame my question correctly