Withdraw collateral

First of all you need to choose on which account you want to withdraw collateral

After you need to click on "Manage" button on the collateral you want to withdraw

After you need to click on "Decrease" button

Then you should write an amount, how much you want to withdraw (1) and then click on "Decrease" button (2)

Then you should approve this transaction in your wallet

And thats it, you withdrawed your collateral!