Do the train schedules change for the summer?

They don't change much and the actual Swiss schedules are online now through summer at sbb.ch or through the DB link at How to Look Up Train Schedules and Routes Online.

Thanks Laura. I keep forgetting to check the DB link as well.

Cindy, It depends which country.
Swiss trains only change once a year (second Sunday in December). The times up to December 2016 have been available on www.sbb.ch and in printed timetables since last November. Same for Germany.
Italy, on the other hand, changes twice per year, in June and December, and is notorious for not issuing the new times until a few weeks before the changeover.
Either way, the changes will not be dramatic, 90-95% of the trains will be unchanged, with maybe a few differences of a few minutes as they tweak services. It is not like air routes, where whole routes start and stop at a few weeks notice. The tracks, stations and trains are there and the services continue unchanged for years (or decades).
Except, the new Gotthard base tunnel through the Alps (the longest rail tunnel in the world) opens in December 2016, which will speed up trains from northern Switzerland and Germany to Italy.

Thanks Chris. We'll be in Italy before Switzerland, so I'll wait until June to figure out our train schedules there.

Thanks Tom. I've been checking the Venice to Milan Fressia schedule daily as it's already been posted up until the week before we need it in August. We have a few regional trains to book as well, and I expect those to be the ones that are posted later.

I have been spending this evening doing nothing but train schedule investigating. The sbb.ch website is truly awesome. So nice to know not only the times and stops between destinations, but which platforms and the stops before the ones we want so we're prepared to disembark ahead of time. Great system.