Should I clutch when shifting 4 stroke sort bike Yamaha?
Get an instructor to show you how to ride a bike. You do not have a clue right now.
Sequential gearboxes don't need the clutch to change gear, but you have to roll off the gas to unload the box. However it is kinder to the transmission to use the clutch. You carry one around with you all day, so may as well use it unless you <really> need that 1/100th of a second off your standing quarter
You can clutch or you can speed shift without using the clutch. It is your choice. I never use the clutch except when I start off in 1st gear.
Yamaha just has handles.