You can see number of articles about editing and updating Gridview.
In the following article you will find RowUpdating event of Gridview.
From that you will call Update function in the class file in Data Access Layer.
Here is the link to the article :: http://www.aspdotnetcodes.com/GridView_Insert_Edit_Update_Delete.aspx
There is one more link related to updating the gridview
Hope this helps.