How to Modify Stop Loss Order on MT4

First choose the open trade you want to modify the Stop Loss Order for.

Once you have selected open trade - select modify order button and following trade order window popup will appear and you as the trader can use this trade order window popup to modify the Stop Loss Order Level for your new trade.

This pop up includes the parameters for setting Stop Loss Order Level - type in your new SL stop loss level and Click the 'Modify' button to modify the Stop Loss Order to your open trade.

How to Modify Stop Loss Order in MT4