Bicycle component upgrade suggestions

[abec]

I've just purchased a Schwinn Spencer Cruiser from Land's End to use as my grocery / commuter bike

http://www.landsend.com/pp/spencer-cruiser-bike-by-schwinn~237701_-1.html

but was looking to make a few changes to lighten up the bike and speed up my ride- turn it into a secretly speedy 'sleeper' (relatively).

The front chainring: 38t
wheels: 700c x 35
frame: aluminum

Any suggestions welcome =) and thank you in advance!

[DaveM]

A very nice bike. I don't know that there's much you can do to make it a "sleeper" though. Reducing weight will not have a big impact on speed to be honest. But if you want to anyway, look for steel parts that can be swapped for alloy (handlebars, stem, seatpost, seat, rack, etc.)

Probably the single easiest thing you can do to make it faster is to put on high quality tires. Different tires can have very different rolling resistance.
http://janheine.wordpress.com/2012/06/13/bicycle-quarterly-performance-of-tires/