The 'Reject call with SMS' option should be available on your Android version. If you can't swipe from the bottom of the screen while you receive a call to use the option, try to update your Android's version. To do that, go to Settings > About > Software update > Update. It's advised while you do this to use a WiFi network due to the large amount of data that can be downloaded for an update.
Also, try going to Settings > Call. There you should find all the available option for your device regarding the rejecting a call with a SMS. If the option is still unavailable, you can try to use an application with the same functionality. I recommend you take a look at Smart Call Control. This is fully compatible with your Android OS.
