Presuming it's a copy-protected Blu-Ray disk, first use MakeMKV (http://www.makemkv.com) to rip the Blu-ray to an unencrypted file.

Then use Handbrake (http://handbrake.fr) to compress the file to a size more suitable for your tablet.

If it's not copy protected, then you can just use Handbrake directly on the Blu-Ray.