Q&A for How to Remove Website Data from Safari in iOS

It is possible that their tracking is so persistent that you cannot remove it unless you wipe the phone and make a factory reset.

Open up the Settings app, then scroll down to Safari, scroll all the way down to Advanced, select the Website Data Selection and remove them individually (or you can use the All button at the bottom). If the website selection is permanent, consider changing your proxy settings and obtaining a new dynamic IP address (see wikiHow to Change the IP Address on a Mac for instructions).

Launch the Settings app from the Home screen of your iPhone or iPad. Scroll down and tap on Safari. Again, scroll down to the bottom and tap on Advanced. Now tap on Website Data. This is where you'll see all the sites storing data via Safari.

No, but you'll have to re-enter user data on some websites you visit.