Thanks, Thirstywolf and jcl. Both of your advice are very important to me. As I read from Zorro manual, Z5 can take up to 20 trades in a few weeks under some market condition. In this case, if I choose to raise leverage to 1:500, then 20 excessive volume trades will be made sequentially, which is too risky for me.
So it's all clear that I will search for a new accont allowing me to trade more flexible volume.