YOu can't change megapixel of camera as they are fixed but yes there are some triks to improve camerq quality :-

​Choose Camera frame as standard because full_screen will reduce the m_p amount.      Standard = 16m      Full screen = 11.xx mp
2.   Use HDR mode to increase depth         in your photos.
3.   Try using other camera apps other        than stock app like
      Google Camera           https://qsf.ec.quoracdn.net/-3-images.new_grid.external_link.svg-26-aef78ead48f1f1e2.svg"); background-position: 100% 0.3em; background-size: 10.5px; background-repeat: no-repeat; background-attachment: initial; background-origin: initial; background-clip: initial;" target="_blank">https://play.google.com/store/ap...       camringo  https://qsf.ec.quoracdn.net/-3-images.new_grid.external_link.svg-26-aef78ead48f1f1e2.svg"); background-position: 100% 0.3em; background-size: 10.5px; background-repeat: no-repeat; background-attachment: initial; background-origin: initial; background-clip: initial;" target="_blank">https://play.google.com/store/ap...  (its a paid one)
4.    you can also buy camera lens       availabe for your device from                market if you really want some       Subperb quality photos. But it is a       costly option.