Mod/ROM will not work. Your best bet for the HP Slate 7 2800 is to do the following.
Install Wondershare Mobile Go on your PC and use the free 5 day trial
Root your tablet with this program. It is very good just make sure the super user app that it install, make sure you grant permissions. If you have trouble with the root...just watch your screen when it says Grant Access and say yes. Later I go into Super User and allow automatic access without the prompts.
Install ClockworkMod 6.03 by putting it on the SD card in your tablet but activating it on your PC by going into my computer and clicking on the program application.
Then install Uninstall app from google play (Root) and it will help suggest certain bloatware programs to get rid off.
If you see some kind of china application (not written in english) ..get rid of it.
As far as going to KitKat...forget it. Or Lollipop...all those MOD and Programs are full of a malware. Do not use any programs from China. There are no MODS or ROMS...all those links on google are fake.
At least you have a rooted device.