If you just installed WP Popups you will get a notice in your dashboard to import the legacy popups. To do that you need to go to WP Popups -> Tools -> Import and choose the popups you want to import into the new plugin. The only thing you need to have in mind is that you need to have installed and activated all the needed add-ons. So for example, if your popup used Aweber, you need to have the Aweber addon installed and activated before importing the popup.
Once you hit the “Import legacy popups” button, all popups will be imported as a draft into the new plugin. You need to go and check that everything it’s correct, content, display rules and settings before hitting the publish button.
When the popup it’s imported a new ID it’s generated. So the trigger class will change again and you need to update your pages in case you are using manual triggering. If you are using class attributes for class triggering you could simply add a new trigger rule to the popup and use the old trigger number. So if your old popup ID was 123, you could trigger your new popup using that ID by adding a new trigger with ID spu-123:
If you were using href attribute trigger such as #spu-123 I’m afraid you will need to update your pages. For that task you could use a plugin such as Better search replace.