There are several issues affecting how loud it will sound.
Computers often have multiple places to change the volume - check the instructions for the tablet and ensure that the level is turned up in each place.
Digital audio has an absolute maximum peak level - 0 dB. That’s when the waveform touches the top or bottom of the track. Attempting to get a higher peak level than that will cause distortion (clipping).
Not all sound with the same peak level will be the same “loudness”. If you compare a dance music track that has a peak level of 0 dB with say an acoustic guitar solo that also has a peak level of 0 dB, the dance music will probably sound about four times louder than the guitar solo. This article explains why: http://en.wikipedia.org/wiki/Loudness_war
Another issue is that tiny laptop speakers have a very limited frequency range and I presume that tablet computers are the same. Low frequencies in particular are played extremely weakly. Bass below about 100 Hz will probably be virtually inaudible regardless of how big the actual signal level is. There’s nothing that you can do about that other than use a better speaker or headphones.
The first thing that I’d suggest is attaching a remote speaker to the tablet. Even cheap little things like this often have much better sound and a much better frequency response than tiny laptop speakers: http://www.amazon.com/JVC-SP-AP300A-Case-Built-Speakers/dp/B0009824MK
If that does not work, then I’d suggest that you apply a “peak limiter” to the audio. A good peak limiter will reduce the relative level of the highest peaks without distorting the sound, thereby allowing the overall volume level to be increased without clipping. Try the “brick wall limiter” here: https://forum.audacityteam.org/t/peak-limiter/20300/1 Instructions for installing plug-ins are here: http://audacityteam.org/download/plugins