Step-1 : Login to Admin and navigate to
Catalog->Manage Products , Now all your products will list here.
Step-2 : Press Check All on left corner of the table view or select any single or multiple records from the table list
Step-3 : Now, you can find drop down with the label Actions on the right corner of the table list, in the drop down list, you can find Delete, Change Status and Update Attributes.
Step-4 : For Attributes to be update, Select the option
Update Attributes and press Submit button. Now, a new window will open with the fields Name, Description, Inventory, Websites ….etc, you need to update the fields which you want to update.
Step-5 : Now, open Websites tab and click checkbox for each websites to add Product To Websites also Remove Product From Websites
Step-6 : Click on the Change checkbox below each field to update, and enter values on corresponding fields and press Save , you are done.