It's easy to replace old storm windows. Here's how. Loosen all screws and pull the old storm window away from the window frame. Scrape old caulking from the window frame to make sure that it is clean and smooth. Apply a fresh bead of caulking to the frame and press the new storm window into place. Secure it with screws and make sure that all weep holes at the bottom are clear so that rainwater will drain out.
For more on windows, consider:
How To: Select Storm Shutters
Buyer's Guide to Replacement Windows
Affordable Indoor Window Inserts Promote Energy Efficiency