First of all check that there is nothing blocking the speaker, could be dust or fluff,
The sound will only go as loud as the tablet allows. At least for the built in speaker(s). The only other thing you can do would be to use headphones or external speakers connected through the headphone jack that would have their own volume on top of the tablets volume.
You could also turn the volume up to full with the rocker button and go into the android's settings , into Sound or Audio settings /profiles, In this menu you can individually change the volume of notifications, ringtones, system sounds, and media. Increase the sliders to their maximum volume by either moving them all the way to the top or all the way to the right.
Yes there are apps available on Play Store however these can blow the system speakers.
If none of this helps take it back to the store and tell them it has faulty volume,