Hey Sandy,
I just went through a similar project to rename SFDC Campaigns and Mkto Programs. To my knowledge, there is no way to merge Campaigns. It might be quicker to just rename your existing Campaigns that are already synched, which is what I did. You can create a spreadsheet with the SFDC Campaign Id, the existing name, and the name you want to switch it to. This will go much quicker that changing each campaign one by one.
Is there any other information in the newly created Campaigns that you need? How many campaigns do you have?