at the start of your app check the available version, the you can use an AlertDialog to ask for the upgrade.
Read this::
Is there a way to automatically update application on Android?
and this is an AlertDialog example::
if (ConfigXML_app_version> myapp_version){
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Upgrade");
builder.setMessage("Update available, ready to upgrade?");
builder.setIcon(R.drawable.icon);
builder.setCancelable(false);
builder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
Intent intent = new Intent(Intent.ACTION_VIEW ,Uri.parse(app_link));
startActivity(intent);
finish();
}
});
builder.setNegativeButton("Nop", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
dialog.cancel();
}
});
AlertDialog alert = builder.create();
alert.show();
}