Typically the problem is that the survey has not been updated after you made changes. In this case the changes will only be saved as a draft and are not visible to the respondents. The process of updating a survey is practically the same as when you first release it.
In the Build tab of your survey click on Update... at the top of the screen, then on Update changes. You can update your survey from the Deliver tab as well, there will a Changes available... text next to the Online slider at the top of the screen if there are unreleased updates.
After you've updated the newest changes all methods of responding to the survey will immediately lead to the new and updated survey. You can test your new updated by copying the default share link and opening the survey in your browser. If you want to send more invitations you can click on View delivery options... to go to the Deliver tab and create new invitations.