Simplest is to copy everything to a computer or microSD card. For cloud backup you have several options.
If you install/open the Photos app, you can backup your photos and videos to Google's cloud storage (tied to your Google account). It will automatically backup photos and videos as you take them (you can opt to restrict backups to WiFi, to save cellular data), and you can view them from or sync them to your new device. The drawback is that Google only allows unlimited storage of photos up to 2048x2048 resolution. You have to enable full-size backups to backup the original-size photos, and their file size will be counted against the 15 GB of free storage Google gives you.
If you subscribe to Amazon Prime, it includes unlimited...