Click the Import Catalogue button 
and select the .onz file that contains the Once Catalogue you wish to import.
You can choose to import parts of the catalogue by selecting items from the tree displayed in the dialog,
In the dialog you have the options to:
- Import product data only.
When this is selected it will not import any of the % price changes that may have been saved in the catalogue. - Replace existing items.
You need to check this if you want to overwrite the selected products, prices, and ranges that have the same name in your current catalogue.
Clear (delete) your catalogue
Sometimes you may want to clear your catalogue, you can do this from the File menu. This allows you to start from an empty catalogue when importing a new catalogue or when creating your catalogue from scratch.
Exporting a Catalogue
Once catalogue files can be created by clicking the export button 
and selecting the parts of your catalogue to be exported. This is then saved into a .onz file in a folder that you select. The default file name includes the date but you can change this if you prefer.
and selecting the parts of your catalogue to be exported. This is then saved into a .onz file in a folder that you select. The default file name includes the date but you can change this if you prefer.It is a good idea to export your catalogue after you have made changes so you have a backup you can restore from. Saving the file on a cloud drive such as Google Drive or Dropbox means you can restore your catalogue even if your PC or hard drive fails.
Note that Since Version 3 of Once Setup, there is a Tools menu option to "Download your last uploaded product data".
This is useful if you have replaced your PC or want to use Once Setup on a second PC.