No, you can't install a different version of Android unless you root the device and find a custom ROM that somebody developed for that specific device -- the forums at XDA-Developers.com is a good resource for that kind of thing, but I still wouldn't recommend it for a novice. If you root a device, you can also uninstall preinstalled or system apps, but that can also get you into trouble, since some preinstalled apps may be necessary for certain basic functions, and uninstalling them might cause problems.
Apart from rooting, you can also go to Settings>Apps, tap Menu>Show System, then select one of the unwanted apps, and see if you can Disable it. Disabling uninstalls all updates, then prevents the app from opening into RAM or updating from the Play Store. Since updated apps are often larger than the original app, this may save you a little bit of space.