european train systems may run differently than how you are thinking, u.s. - style
for example the EC train may be the next train on the same platform! so, you are not running around, just get off, wait, and there it is
or- it's awaiting you just across the platform
you can ask in krakow which platform you arrive in, and from which you depart
(how's your polish??)
of course, it could be you shlep bags down a flight of stairs, over 8 platforms, and up a flight-but i bet there are others doing the same thing so you won't miss the connection- that's why it's a connection
but a word of warning, if you are not used to trains:
verify in krakow which katowice cars are going to prague
otherwise you may get on a train only to discover that it splits down the rails a piece- and part is off to frankfurt or vienna
(some cars will have the itinerary or destinations posted outside)
watch your luggage!
watch your luggage!!