Open the query in design view.
Click the icon that has two sheets offset to the lower left and a down
arrowhead.  Select Update Query.
Fill in the Update To: row with the new information for the fields you want
to update.
NOTE - Always run it as a select query to determine that the records
returned are indeed to be updated and not all records in the database.

When you open the query in design view, in the menu bar select  Query you'll
see a list of query type to change your query to
Update query , append , create table , Select query

Select the update query, you'll notice that the design will change, and on
the buttom you have a row were it say, update to: enter the values there

Before you try anything Bak up your data