Go to https://www.kucoin.com/ucenter/signin and Log into your account
You should be brought to a similar page like the one below.
I'm going to assume you have some BTC in your wallet.
Click "Transfer" in the Main Account block.
Make sure it says its going from Main Account to Trading Account and fill out the other fields.
The BTC should be in your Trading Account.
The next step is to click "Trade" in Trading Account block
You will be brought to a similar page.
Next click BTC/USDT and search for STX and click on STX/BTC.
Now in the bottom right of your screen click "set trading password"
Finish creating your password and don't forget it. You'll need it later.
Once you're brought to this page, make sure to enable either "Google Verification + Email Binding + Trading Password" or "Phone Number Binding + Trading Password"
Next click Markets and search for stx and click on STX/BTC
Enter your 6 digit Trading Password you created earlier.
Now click Spot, then Market.
Then click one of the percentages. If you want to use 25% of your BTC, then click the 25%. If you want to use 50% of your BTC, then click 50%. If you want to use 75% of your BTC, then click 75%. Most people will use 100% of their BTC, so click on that one or the one you want to use or enter the amount that you want to use, and then click the Buy STX button
Make sure your order is successful
In the right corner of screen, go to Assets > Trading Account
In the STX row, click "Transfer"
Send your STX from the Trading Account to the Main Account and fill out the required fields.
Make sure Main Account tab is selected and click Withdraw
Fill out the required fields: Wallet Address, Network, and STX Amount. You can leave the Memo and Remarks field blank.
Confirm your transaction with the security measures you selected earlier.
Check your Hiro Wallet and you should have your STX.
You did it!