How to "merge" households via the individual household screen.
While you can't completely merge two households together, you can effectively merge the households by moving the uploads contained there.
You'll accomplish this by first heading to your client's household page. Then, you'll need to click the small ellipses (...) to the right of the upload under the heading "tax returns."
You'll then select the household you wish to move the upload to. Then, delete the "empty" household.
*It should be noted that you will not be able to move any standalone scenarios or Tax Letters to other households at this time.
Once you've moved the uploads in the process outline above, you can add the taxpayer that you've merged to the new household by clicking "create" under "clients." 
If you wish to edit the household name to include the new taxpayer, that can be done by clicking the edit icon at the top of the household screen as shown below. 