the usual answer:
change wireless channel
the width from 20/40 to 20 oni (or something like that)
if u broadcast b/g/n try only g or only n (depend what device u hv la, if all n
just n no g/b).

in ur screenshot, change this settings:

channel bandwidth set to 20

channel: set to 3
extension channel: set to 7 or 6? it should only allow valid value...
try other combination but dont try channel 1 or channel 6 or the last one.... bcoz this is the default on many router... dun use them so no interfer with other device

and the other settings also.... read my reply completely.... good luck

yea i think must be 6 channels apart.. so the router choose for u lah dun worry bout it

so after all change how the performance now? improve??

no, like i said leave it at 3

extension set auto no problem