But that's only dirty hack, not the proper way to code.
The proper way is to divide operation and display (at least, MVC is even better). This way you can set some variable indicating name was changes and generate a page from template based on that variable (ie with success msg set on top of page if there is one).
Please don't make your own template engine. Use some existing ones instead (Savant is quite easy to learn).
Edit: Ok, I won't give you ready-to-use code, instead I will tell you how to do it the quick-but-dirty way:
1) create a div in which you want your message to appear, place it wherever you want it to be and give it some id (unique in page scope) ie:
It's quick fix but don't get used to it. Instead learn how to do this the right way. You can start with https://github.com/phplucidframe/phplucidframe/wiki/Integration-of-Savant,-The-Simple-Template-System or use other templating system. It will save you many bigger problems than this one in future :)