How to safely shut down or force shut down Sigma Mobile devices

Sigma Mobile X-treme PQ52 Sigma Mobile X-treme PQ52
Sigma Mobile X-treme PQ53 Sigma Mobile X-treme PQ53
Sigma Mobile X-treme PQ54 Sigma Mobile X-treme PQ54
Sigma Mobile X-treme PQ37 Sigma Mobile X-treme PQ37