Some users experience their tablet seeming to run slower after a few months than when they originally got the tablet. The simple reason for it is what is running… Without you knowing it you may have dozens of apps running in the background on your device, this is eating up battery power and processes making your tablet run slower and last a shorter time between charges.
You can see what apps are running in the System Monitor tool (from Apps > Running). If you recognize apps that are running that you don't ever use, uninstall them. If you see apps that you don't use very much, check in that app settings to see if you can disable to background task.
If all this doesn't seem to have an effect you can reset the tablet very easily from the repair and formatting section of the Settings Menu. Resetting the tablet to factory settings is easy and quite fast (it'll take less than 20 min) and could save you a call to customer support or a return. Though it does mean that you may have to re-download some apps and retransfer your media to the tablet.