Lua How to make a promotion with click?

[RaikND]

I got this script

function onUse(cid, item, frompos, item2, topos)
     doPlayerAddPremiumDays(cid, 30)
     doPlayerSendTextMessage(cid,MESSAGE_INFO_DESCR,"You gained 30 premium days.")
     doSendMagicEffect(topos,27)
     doRemoveItem(item.uid,1)
end

But i dont got idea how i change for make it for promotion, any can help me? thanks

 

[Acubens]

function onUse(cid, item, frompos, item2, topos)
    
if getPlayerVocation(cid) < 5 then
		doPlayerSetVocation(cid,getPlayerVocation(cid)+4)
		doPlayerSendTextMessage(cid,MESSAGE_INFO_DESCR,"You are promoted to "..getPlayerVocation..".")
		doSendMagicEffect(topos,27)
		doRemoveItem(item.uid,1)
    else
		doPlayerSendTextMessage(cid,MESSAGE_INFO_DESCR,"You are already promoted.")
	end
		
end