How can I change image names automatically?

I have about 1,200 images that I need to rename them by adding a name in front of the current name. The name to be added is in an excel sheet in the same row as the current name.How can I change image names automatically?
In a third cell C1 enter the following

=A1%26amp;';_';%26amp;B1. A1 is name to be added to existing name in B1 with an underscore between. This can be changed to whatever you like or dispensed with altogether. Copy down to the bottom of your data list.