Navigate to the Invest tab
Select the Mirrored Asset that you wish to sell
Click Sell (note: the Sell option is only visible if you do have available quantity to sell)
Enter in the amount to sell (in mAsset), and click Next
Review the amount, price, fees and total cost. If you need to change the order quantity, click Reset Sell Order and enter the new quantity.
Click Confirm to place the order
Review the executed Sell order amount (in UST) and click Done