Q: Hi I have apps with an older Apple ID user name which I can no longer access how do I change that so I can update them in my new Apple ID (this one I'm using)

Delete and redownload those applications.

(111110)

Click here and follow the instructions.

(111112)

Hopefully, that will work for you; do note this though (since you said you have a new Apple ID and anything you obtain at the app store is tied to the Apple ID used to obtain it):

If I have already downloaded an app from the Mac App Store, can I redownload it for free?

Yes. You can redownload apps from the Mac App Store as long as the app remains available. You may be asked to enter the Apple ID and password you initially used to download the app.

from this Apple FAQ:

Mac App Store: Frequently Asked Questions (FAQ)