Matching Cells And Replacing Data

We have a report with 2 different sheets. On sheet one there are 13,000 rows of data and columns A-H are filled with different data. column A is our item id and column G has a date that states when the item was sold last. Well, the date in column G is wrong for about 7800 rows and needs changed.

The second sheet in the file is the 7800 rows with just the item id in column A and the correct date in column B. We are looking for an easy way to replace the rows in the first sheet with the correct information from the rows in the second sheet without manually replacing it line by line.

I almost forgot to add in, that in both sheets, column A with the item ids are the same item ids on both those sheets. So column A on sheet one has 13000 rows and included in those 13000 are the 7800 item ids on sheet 2.

We tried using the VLookup function that is incorporated into excel but had absolutly no luck, mostly because we have never used this function before. Sheet one already has all the lines of sheet 2, its just that sheet one has the wrong dates for the item ids and sheet 2 has the correct dates. im trying to replace the dates on sheet one from the dates on sheet 2 matching on the item ids from both sheets......