I'm using webform 7.x-3.20 version and I want to to upgrade it to 7.x-4.x, but I've 7 to 8 existing webforms whenever I update this I'm losing my previous webforms cause of changed table structure. If is there any easiest way to update then please let me know. It'll be appreciated.
In the comment section of the documentation there is written:
Note that you must be running the latest 3.x version of Webform (for either Drupal 6 or Drupal 7) before upgrading to Webform 4.x.