H4 to h1 -in US

[soma2006]

Hi,
My query is
i entered US on h4 and then changed thru a company who filed my H1B. But 4 months have passed i hvnt been able to get any project.
-my query is till how long one can be on bench in US?
-can i retrain from another company and get my H1B transferred?

any feedback will be well appreciated.