Using Migration Assistant

I want to transfer (clone?) the contents of the HD on my MacBook Pro (15-inch 2016) to my iMac (27-inch Late 2013). Both are currently running OS 10.12.6 because the old Quicken 2007 won't work on anything more recent, and the new Quicken is useless to me. (I bought the iMac primarily to use as a larger monitor for the MacBook at my desk for viewing B-size drawings, and it has performed that function well.) However, I would like to keep the iMac for Quicken with 10.12.6 and update the MacBook to a newer version of the OS to take advantage of the recent changes.

I've previously tried to use Migration Assistant to move the MacBook contents to the iMac, but after tallying up the size of the move, MA reports that "There is not enough room" on iMac HD. So it appears I won't be able to make the transfer unless I edit the material to be moved or make more room on the iMac. Both computers have 2TB SSDs, and I don't want to lose any legacy content from the MacBook, so I would prefer to remove - or erase - some of the data already in the iMac HD to make room for all the data from the MacBook.

How should I best go about doing this?