How to do factory reset without deleting any thing

@pijush you will have to delete something. At least any offending third part app. You can't do that with a factory reset. That will delete all of your files, Your phone will be the day you bought it from the store.

Either you backup all of your files (pictures/Music/SMS/contacts etc.) and then do a factory reset (remember you need your Google account password and the same email as you used when you setup your phone), or you try and delete the apps that cause the pop ups.

I would try and start the phone in Safe mode. Then check to see if those pop-ups still happen. If not, you know it is a third party app. Now delete those that you have installed one by one until you find the one that is causing it.

Here are the instructions on how to place it in safe mode.

Now, you are not telling us what pops up. If those are pop up messages, try to stop them by:

"touch & hold the notification, then touch Turn off notifications. To review all apps and adjust whether they can send notifications: Swipe down to view your notifications from here.

See if this will work to turn off any pop up ads

Turn pop-ups on or off

1. On your Android phone or tablet, open the Chrome app .
2. To the right of the address bar, tap More. Settings.
3. Tap Permissions. Pop-ups and redirects.
4. Turn off Pop-ups and redirects.

More on that over here