Can direct switch or need to port to prepaid first?

I see. Thanks.

I prefer to go to centre for matters like this, easier to ask if anything surfaces

I'm at digi store sunway piramid now.
They said cannot they cannot change just like that, there's no option for them to do so.
The only way is to port out to another telco, or change to prepaid, then wait one month, then port in back or change back to this plan.
Which is very sucks.