Mass Update

I have imported 2000+ contacts from Outlook (via comma deliniated file), and succesfully imported. We might have 30-50 contacts from one account name (hospitals are our marketplace), and when they were put into outlook the the account name was not always entered the same way. For example: Miami Childrens Hospital vs Miami Childrens. This has created a problem when entering the account name, and then finding associated contacts....as there may as many as 8 different accounts created for that one hospital. I attempted to do a mass update of the account name, by quering the email adresses for people at that hospital (they all have the MCH.org ext) Once I have a list of the 30-50 contacts that meet that criteria, I do not have the option to choose the "account name" as a field to mass update. Does anyone have an answer to this.