How hard will it be if I quit my job and take an interest in online jobs?

Tough. Its takes months to build up enough online income to truly support yourself. it also takes a lot of dedication and hard work. There is definitely work online and you can eventually make a living doing it but its not something that will happen overnight.

Rightly said and it also takes more time to learn online things isn’t it? there are also many scam sites running around which makes things still more difficult. But since i have some technical knowledge i think i can find some good projects which i can handle it sitting at home

I have made up my mind to spend full time in online jobs as there is enough pressure in my office which i cannot handle and things are becoming worse day by day.So, i feel online job is an alternative for me

You should check out sites like Elance, Freelancer and PeoplePerHour, they have jobs you can bid on and make some great mony. A dear friend just won a $2500 ghost writing job on Elance. I won a Getting card illustrator job from PeoplePerHour, a Graphic art comic job from Elance and a I did 78 articles on pets for a job I got off Freelancer, plus a few others. I took a bit to win my first jobs, but once you get the first one under your belt it gets easier. Good luck!