Depending on the components on your bike there may not be any reason to upgrade your components - just some maintenance, replacement of cables, pads and tires/tubes.
But- if you want to do an upgrade it certainly is possible!
Right now I am looking at either restoring my hubby's late 1970's era Fuji 12 speed -
or putting together a new bike for him.
He's a LOT bigger now than he was then!!!
althought the Fuji has a 24 inch frame -
which is certainly huge!
He's expressed a desire to get back into road racing so I am going to encourage this all I can..he is getting a full kit for Xmas- shoes, shorts, jersey -Clydesdale sized! - helmet - a nice Giro one- perhaps he'll wear it...
and either the Fuji refurbished like new- or a new bike with mid range Shimnao 105/Ultegra components.
Do your homework- there is lots of info on the web.
Good luck!
Kimba
Bicycling magazine had an issue this summer dealing with components - you might try to get the back issue.
Email me if you have any questions- I've now put together some 5 bikes! - upgraded an old mountain bike - put together 4 others from scratch- and even put together a cool BMX bike!
Whe you come to the end of all you know-
and you are about to step off into the darkness
faith is knowing one of two things will happen-
there will be something solid to stand on-
or you will be taught to fly...