Would be easier to change the  back freewheel.  If you can get a 11-30T or something similar, that would give you a much better top speed. Ask a few kakis here who has just bought on TaoBao.

This bike of yours, to mod, you'll have to spend $$.  If the 11T is still not fast enough, then you'll need to change the crankset and bottom bracket.

These Dahon ones are one piece so can't just change the chain ring.....   My Speed D7 is the same, but mine's 52T, so ok 

one piece de meh?  even those china bike like trinx can remove the chain wheel,
but anyway, got 56t crank set at taobao for RMB190 only...
sure kenot get here...

if can remove, bcd 110 130 can get a lot.....