IT ALMOST WPRK IN 90% DEVICE TO ROOT
Step:1 download frameroot (for samsung users) and kingroot (for other phones) click here framaroot or Here kingroot suitable verson to your phone
Step:2 install it and open it
Here step by step for frameroot on samsung with figure
Step:3 click on framaroot
Step:4 make sure that the option in install supersu
step:5 choose any one option second is good if its fail than click on first one
Step:6 now when its sucessfully done you reboot your phone waight for rebook and ur mobile is rooted
Of this do not help than use king root its 100% do it try two times to root with kingroot if fail good (good internet connection is required while rooting it donot hamper when root is interrupted )
If this is helpfull for you please write on comment please