Transfer Apple Developer Cert to a new Mac

So, I have signed my apps and sell some on the Mac App Store.

I recently upgraded from my old five year old MacBook to a new 13’’ Retina. My old Macbook has the certificates on it. Well, the hard drive I removed from it has the certificates on it. I see in the apple developer center I have some certificates listed. I tried downloading them and installing them in keychain, but that doesn’t work. Can I just delete the certificates on the website and begin the process anew? I don’t want my existing app to have terrible repercussions though.

I seriously need a dummies guide to this cert business.

I think you must download your current certs from your apple developer account and install it with a double click. It is the same way like you get a new or a new valid cert every year from apple.

With the latest xcode this is very simple to do.
You only need your app dev account email en password. Xcode installs all certsfor you. No need to backup/copy files manually.

Indeed Christoph’s suggestion is the way to go. With Xcode Apple have really improved the whole certificate setting up process.