Will my custom presets be lost if I use the uninstaller? How can I save them?

This information applies to version(s): 4

If you install Nik Collection by DxO over a previous version of Nik Collection by DxO, presets will be migrated automatically to Nik Collection by DxO. If you choose to use the Nik Collection by DxO uninstaller to uninstall a previous Nik Collection by DxO version, be sure to check the checkbox to keep custom and imported presets, or they will, unfortunately, be lost. 

Please also see this article:

https://support.dxo.com/hc/en-us/articles/115015301507