Erase and start over

Erase this device's copy of your library, or delete the copy in iCloud. Your license stays active either way.

Mac: Settings → Data
iPhone and iPad: Settings → Sync
On: Mac, iPhone, iPad

Erase this device

Erasing deletes the library on this device for good, not to the Trash, and starts Resurf empty. Sync turns off on this device so the library doesn't download again. Your iCloud copy, your other devices and your license aren't touched.

Open Settings (⌘,), choose Data, and click Erase… beside Erase this Mac.
Read the line at the top. It says whether Resurf found another copy in iCloud.
Tick the checkbox and click Erase this Mac, or Erase everything if no iCloud copy was found.
Resurf restarts into first-run setup.

In Resurf's Settings, tap Sync, then Erase this iPhone (Erase this iPad on iPad).
Tick the checkbox and tap Erase this device, or Erase everything.
The app closes. Open it again to start fresh.

Delete your iCloud copy

This removes everything Resurf keeps in your iCloud and turns sync off on this device. The captures on this device stay.

Open Settings (⌘,), choose Data, and click Delete… beside Delete iCloud data.
Tick I understand this can't be undone and click Delete.

In Resurf's Settings, tap Sync, then Delete iCloud data.
Tap Delete to confirm.

Other devices that still sync keep their copy and may upload it again. Turn sync off there too if you want it to stay deleted.

Questions

Does Erase this Mac delete my iCloud copy?

No. Use Delete iCloud data for that.

Can I get my library back after erasing this device?

If your iCloud copy is still there, yes. Turn sync back on in Settings → Sync and it comes down again.

Is my license kept?

Yes. Neither action touches your license.