Update Multi Pick List Options

Update Multi Pick List Options

I have a multi pick list in the leads module that list my products. Lets say there are 3; Widgets, Bits, and Bobs.

I want to change the product names to Acme Widgets, Acme Bits and Acme Bobs.

I had hoped that by renaming the Pick List options, all existing records would update to have Acme in front of the name, but it didn't work. 

Does anyone know how I can update the picklist and all existing records using the pick list with the updated names please?

Thanks,

Braden