Samsung introduced Galaxy S4 in two different models in international market. One is I9500 and the other is i9505. The only main difference is about CPU. I9500 is powered by a Quad-core 1.6 GHz Cortex-A15 & quad-core 1.2 GHz Cortex-A7, and I9505 is powered by a Quad-core 1.9 GHz Krait 300.
So, do as follows to see what S4 model you already have:
1. Open "Settings" App
2. Go to "More" Tab and find "About Device"
3. There you should see the "Model Number"
Read More Galaxy S4 Tips and Tricks