Tire swap might depend on how wide the rims are, but it should work and should cut a lot of weight. Changing the chainrings ... two ways I can think of. if the bolt pattern and size is the same, you could just bolt the new rings to the spider (the arms extending out from the drive-side crank.) Probably you can look online and fine the bolt pattern for your crankset--find your BCD (bolt circle diameter) and make sure the new rings fit (http://bloombikeshop.com/articles/ca...ng-bcd.php---I found this online but there are liely better resources.) If you find rings that fit, changing them is a matter of a few bolts.

Otherwise you will need to install an entire new crankset, for which you will need to invest in a crank puller, which is $10-$15 on most websites and really useful to have if you want to do anything with bikes beyond riding them. (Of course you will need to buy a new crankset--or is it chainset?)

Word of caution---if you buy an entire new crank, it might not fit the existing bottom bracket. if you have a good relationship with your LBS, you could ask, or ask online. Otherwise you might need to also replace the bottom bracket, which is another $15 tool plus the cost of the bottom bracket.

All of this work is really easy to do, and there are a ton of online videos showing exactly how, step by step.

Other people on this site know a lot, and probably if you post your current make and model chainset, they will be able to tell you all kinds of stuff.