Welcome to Android Central! It depends on what kind of device you have. Devices on Gingerbread are pretty old, so it is unlikely that the manufacturer or wireless provider would have released an official system update to Jellybean for you. But you can always check by going to Settings/About Device/System Update.
The other way is to root your device, which is a process of gaining complete control of the system. The process of rooting varies with the device, so it is important to know which one you have. Then search these forums or others for posts about rooting it. Once you've rooted a device, you can then flash a custom ROM, which means that you are essentially putting a whole new Android operating system on your device. There is no guarantee that everything will function correctly, and you do run the risk of irreversibly damaging the device if you do something wrong (or if the ROM doesn't work well). Rooting a device also voids the warranty, but for an older device, that is probably no longer important.