You don't have to delete your survey to make it invisible to respondents (and please do not delete it because then you also delete all the data!). Taking it Offline means that it will stop gathering data while you still have access to its settings, reports, and data.
You can close the survey anytime. That means that your respondents can't see the survey anymore. Respondents still answering the survey, however, can still complete the survey.
This is how to close the survey:
On the home page click Surveys and you will see all of your surveys. Open the survey you want to close by hovering the mouse over the survey and clicking the arrow.
If the survey has been online, you will see the following view:
Click the circled tab Online and the following window will pop up.
If you are sure that you want your survey offline, click the Set offline button. Notice that putting a survey offline will pause all the share links.
If the survey is closed, the survey will look like this for the respondents who open the survey link:
If you want to open the survey again, open the survey on the Survey page and click the Offline button.