[AccessD] Update query copy one field to another

I'm just not getting it. Writing SQL statements is not coming to me, so explain this in what I type into the grid view.

Table name - tblCemeteries4Updating
Field name - Surname
Field name - MarrName

In the update query grid, I have 

Field		MarrName			Surname
Table		tblCemeteries4Updating	tblCemeteries4Updating
Update To

What do I type into Update To grid in order to copy the contents of MarrName field into the Surname field? 

(I don't want to change the Surname field to MarrName, as I need both - after doing this copy, I have to manually go through and del the contents of MarrName from all the males, and add the correct MarrName to all the females, as all the existing contents are "maiden names"}

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Kathryn Bassett (at work address)
kathrynatgwens at socal.rr.com
kathryn at bassett.net (home)