how to change the Diff Pair trace widht ??

Hi ,

i set the differential pair for my design.i could not change the trace widht for assigned pair.in default i keep min trace width is 4mil and max is 25mil.if i assigned differential it is automatically assigned tracewidht as 6mil i need to change the trace width as 5.6mil how to change tracewidht and even i could not keep tracewidth 4.5 mil for inner layer.i got error how to clear it