changing from 3rd generation to new 4k apple tv, want to get all from original onto new.. how do I do that

Plug it in.

The AppleTV box itself doesn't store much locally - everything is stored in Apple's iCloud servers and as attached to your iCloud account.

When you fire up the new AppleTV, configure it with the same iCloud account used on the old box and it should synch everything back up.

The 3rd gen didn't run any apps, it used pre-set channels that were sent via server. With the 4K model it is using native apps, some are pre-installed from Apple and then you can choose exactly what 3rd party content you download from the app store.