Where to change country information at Samsung App Store?
Do as follows: 


Go to Settings &rarr; Applications &rarr; Samsung Apps and then tap the clear data and clear cache buttons.
Back to all applications, find Samsung Apps and click on it. Select now the correct country.


Note: The correct country should be where you currently are, or the country in which you registered first. Try first country first, and if it is still does not work - simply repeat steps 1-2 above with the other country.

Hope it works for you!