I just purchased a Toshiba Excite AT15-a and it cannot update past Android 4.2. I want to run an app called 'GranBoard' and it required Android 4.3 and up. I see that you can flash a custom ROM to get it up to Marshmallow. I started to try the process with OmniROM and when taken to the download page, there are countless ones to pick from. Can anyone help me decide which one is correct or maybe provide streamlined directions to do this?

 

I found this site, but the download links for the .rar files are dead.