How to bulk change one value to another in a single field?

If you want to do all of them, run your "List All" report.  Then at the upper right, below the table ribbon will be the word More with a caret to its right.  Click on the caret and one of the options should be "Search & replace in this report. 

Choose the field then the from an to fields and click Next.  Then it will tell you how maby records will change and when you click Ok it will change them