Change Instrument Programs Using Keyboard?

Is there a way to change the instrument program of a softsynth using the keyboard?

Not with the ordinary keyboard no.
If you have a Midi keyboard, then program changes from the Midi keyboard are directly routed towards the VST plugins. As long as you have the program changes checkbox enabled in the Midi preferences that is:

You can also make automatic program changes by using pattern effect commands to perform a program change using the C2 command in the panning column of the most right note-column in a track.
http://tutorials.renoise.com/wiki/Pattern_Effect_Commands#MIDI_Commands

This way if you need programchanges in our live events, you are able to preprogram these and not have to worry to make the change manually.

Thanks for this. I’m able to get C2 working. Is there a way say which program bank either through the pattern editor or lua?

With the required CC command, but that can differ for plugins. I would recommend reading through the manual of the plugin to what CC message it listens to for bank changing.
The same manual link in my earlier post still gives you some directions for this but not specifically because of the difference between which plugin accepts what message.

An alternative method that would allow you to use the QWERTY keyboard would be to host the instrument in a VSTi or AU version of Bidule, loaded into Renoise. In Bidule you can then create a keyboard shortcut that changes the instrument’s presets. I think you may also be able to change the bank this way, but I don’t have Bidule in front of me to check.

Will try to remember to check this later in case you’re interested. Anyway, you’ve sparked my interest so I’ll probably check.