Flash custom rom via pc hanap ka sa xda developer ng custom rom if meron para dyan then after flash vulnerable to root nayan using one click root app such as kingroot or kingoroot
Easiest method, download kingroot. Siya na magchecheck and titingin kung compatible for root. And just one click to root. Rooted kana.
Search mo nalang kingroot sa google then, download mo yung apk for android.