Android Question Application install fails

[Mostafa86]

Hello, I'm a beginner in android, in fact I need to run and compile an application as part of my project and will be back to electronics part and my domain, the problem is: I have the source code, I run and compile it successfully, but while installing the application i get this error:
I send the screen shot.
Thanks for help in advance.

 

[fixit30]

Try uninstalling the app from the device first, and then try again.

 

[Mostafa86]

Thanks, I did it, and now works.