How to shift my career and when i should decide that its time to quit my current and search for another one?

After three years in a job, a person usually understand everything and should start looking for a shift either vertically (an advanced position) or horizontally (a different career path). for a career shift you need to acquire enough education or training certificates. 

Well in my opinion when you feel that your level of learning is not increasing any more and you have plan b mean to switch from current job. So you need to Jump and take the risk. Because if you don't you will never know.