Wipe tablet and install new ROM
Basically, if you are already rooted and running a custom ROM, you will want to follow these steps, and I hope you know what they mean, because I am going to try and keep them as simple as possible:


backup any of your data you want. Google does this automatically with some stuff, but the other stuff you can use Nandroid Backup.
Reboot into recovery.
Wipe all data/factory reset.
Flash the ROM in the recovery tool. I use TWRP so I just click install and then navigate to where I have downloaded and saved the .zip file that I want, but yours should be similar no matter what recovery you are using. 
Flash the most recent gapps package in the same way as the ROM's zip. These are the Google Apps that you will need.


That should be it. I simplified it so that you can understand, but if you have questions, leave them below. If this stills seems foreign to you, you might want to look for a video guide on YouTube or something. The process is very similar for almost all phones. Just different files and slightly different methods depending on which recovery and such you use.