If your broker is providing margin, then the answer really depends on the broker you’re using. Contact your broker or the help section of their website to find out how to do this.
A warning: Because bitcoin is extremely volatile, margin can either help you grow your account very quickly or wipe it out quickly, depending on the amount of margin you have and what the market does. For example, if you have 2:1 margin, your account could go up 60 percent when bitcoin goes up 30 percent – or it could go down 60 percent when bitcoin goes down 30 percent.
If the price dips 50 percent, then that might be a great buying opportunity for most people interested in bitcoin. But if you have 2:1 margin set up on your account, a 50 percent drop would wipe out your position. And a 50 percent dip in price is NOT out of the question. If it drops fast, you can lose more than the value of your bitcoin, especially if you don’t have a stop.
Bottom line: I recommend you do NOT use leverage using bitcoin. It’s just too volatile. If you have any leverage on your current trade(s), you might have to close them to stop using leverage. Given the risk you’re already in, I believe that would be worth it.