Generate the impex export script
Go to System->Tools->Script Generator.
In the pop in click on generate. In the textarea you'll then have to export impex for each model.
Copy the models you want to export.
Go to System->Tools->Export.
Paste the impex copied previously and click on save. Click on next then start.
Download the exported impex and the media if there is one zip file.
To import go to System->Tools->Import.
Upload a new media (the impex zip downloaded previously).
Click on next. Upload the media zip. Change the error mode if needed, I prefer use ignore.
Finally click on start.