For the definition of Take-Profit and Stop-Loss limits, see this article: [Margin] Take-Profit and Stop-Loss
Find the trade you want to edit in Positions panel. You will see two small indicators, TP (Take-Profit) and SL (Stop-Loss) surrounding the market price of the trade.
Click on the trade to expand its details, then click on the TP pencil button.
Input the value you want, then click the check symbol. System will ask you to confirm again.