Use an update query
limit the rows processed using a where clause
The query takes the following form:-
Update mytable set acolumn = avalue where anothercolumn = 23
Text/string valus to be delimited with a pair of ' or "
Eg where userid ='JJ2'
Dates values to be in ISO or US format delimited by #
Eg where adatecolumn = #2014/12/25#
But in your post theres a couple of concerning items. Now and Name are reserved words in MS Access /JET. You will probably get away with it but my strong advice is do not use reserved words or symbols for table or column names. It will cause problems at some stage.
As to how you update rows, well providing you can identify those rows you can
I'd rather be riding on the Tiger 800 or the Norton