"I want in future to change the background of my App or to add New Event"
These are hugely different scenarios.
Its pretty trivial to use Parse to change a screen background. Just save your existing background image as a file (eg as a UIImage) in Parse, and have your app download the image from Parse and set it as the background image of your UIView. Change the file and all users will see a new background. You would need to do this when the app loads (or at least before you access this screen), or else there will be some annoying delay when you access the screen with the new background image.
Adding a new event sounds close to impossible, as it involves modifying your code. But your compiled code is "signed", and as such is designed by Apple to be impossible to change without going through the market. Any app which could do that could bypass the market and potentially directly download malicious code. And nor (as far as I know) does Apple provide any support for extending or changing code within iOS. If its not actually impossible, I expect it would be so difficult and require so much knowledge of iOS as to be infeasible for the average programmer.
EDIT: You have now clarified as to what you mean by "Event" in your comments. This is just data which you load dynamically (and not an "event" in the programming sense). Yes you can do this through Parse (and lots of other ways), just read/load the data through Parse. Very easy to do, have you read Parse's excellent tutorial?