The way you do this depends on your situation.
Using apps at home
If you are using the apps at home, got a new device and are planning on using the same account, then you can simply sign in to your account on the new device and download them again for free. You can find out more information about that here.
If you are using the apps at home and would like to share with another family member that has a different account, you can try some of the things listed here.
If you are using the apps at home and have lost access to your account, please contact us with details and we can try to help.
Using apps on devices that are shared with many people
If you are at work and the new device will be shared with lots of people, then according to the licensing agreement, you should buy another copy of the app for use on that device.