i have a mail merge which is linked to excel A.xlsx!sheet1 as source data

I did the wizard and there are a lot of fields being put on the word document and i have save it.

I have another excel B.xlsx which is identical to A i.e same headers in sheet1. only the data is different. for example A has 50 rows, B has 100 rows.

I dont want to re-run the mail merge wizard. Can i just change the sourcefile of the word in mailmerge? the fields items of A.xlsx is equal to fields items of B.xlsx. so i just need to re-point the mail merge word doc to excel B without redoing the fields items one by one again? how to achieve that in word 2007?