Dell9100#configure terminal 
Dell9100(conf)#default interface tengigabitethernet 1/32/1
Dell9100(conf)#default interface tengigabitethernet 1/32/2
Dell9100(conf)#default interface tengigabitethernet 1/32/3
Dell9100(conf)#default interface tengigabitethernet 1/32/4
Dell9100(conf)#no stack-unit 1 port 32 portmode quad 
Warning: Disabling Quad mode on stack-unit 1 port 32. Please verify whether the configs related to interface Te 1/32/1 Te 1/32/2 Te 1/32/3 Te 1/32/4  are cleaned up before proceeding further.
[confirm yes/no]:no stack-unit 1 port 32 portmode quad speed 10g

% Please answer 'yes' or 'no'.
[confirm yes/no]:yes
Quad mode is disabled on stack-unit 1 port 32