Lok Ma Chau - Mong Kok

Hi Guys,

I have to get in the evening from Lok Ma Chau to Mong Kok area, what will be the easiest way?
Take East rail line and change in Kowloon Tong for Kwun Tong line? Whole next day i will spend in HK, so as well I would like to use metro without limits, what kind of ticket should I buy?

Thanks for help in advance!
Charles