Use Stop orders:

When you bet on a market with either a buy or sell trade, you must also set a Stop Order. A Stop Order closes the bet automatically at a price that you specify to limit the amount you could lose if the market price moves against you.

You may adjust the Stop order/ stop level price at any time while a bet is open to further minimise risks and 'lock in' any gains (see next section). The minimum and maximum stop levels will vary, depending on the market you are betting on and the amount of money in your account balance.

Closing a bet position will result in a profit or loss being realised on your account balance.

How to 'lock in' betting profits and minimise betting losses >>