In Magento it is possible to update the attributes for multiple products at the same time using the Update Attributes option.
Navigate to Catalog > Manage Products
Select the checkboxes on the left hand side for products that you want to update
In the drop down menu on the right hand side of the screen select Update Attributes and then press Submit
On this page you can update a number of product attributes, including price, supplier ref, stock levels and assign them to sub sites.
To make a change to an attribute remember to press the change button underneath the text field first.