Save .cp as .cptx to be able to open in CP8?

I have about 100 .cp files created with Captivate 4 and need to save them as .cptx to be able to open them in Captivate 8. My team has CP5, CP7 and CP8 available. I tried to save as .cptx in CP5 but it only gives me the option to save as .cp or .cptl and versions 7 and 8 cannot open .cp at all. Suggestions on what to do?

Thanks!!