A BPO employee, need advice what to do for Ph.d while working

I have been working in BPO industry from last 6-7 years and have I am a B.com passout. Like many others, I also want to want to switch my career but due to my past years of experience in this industry, I am not seeing any success elsewhere so now I have decided to go for further studies, I have joined a night BPO this time as I want my day to be available for my further education. So, I have few questions which I Need to get sovled,

--> How can I get Ph.D degree
--> What are the qualification required for it,
--> Which Ph.D subject will be suitable for me.
--> Can I work at night and study in day but go to give exam only ?