Hey there, Clappi Slipa
When you are asked to enter a pin on your Xbox console, enter a random combination incorrectly three times. This will prompt you to enter your Microsoft account password. Once you have entered your Microsoft account password, you will be able to set a new PIN for your account.
Once you have done this, you can remove the PIN by going to:
Profile & System,
Settings,
Account,
Sign in, Security & PIN,
Then select, Delete my PIN.
This should remove your PIN. You may have to turn off the console by pressing and holding the power button until the console shuts off. This will clear the cache. Then try signing in again and download a game.
For removing a PIN for purchases, please go to Change my sign-in & security preferences in account settings. You should see an option for removing a PIN when purchasing content on Xbox on that page.
Hope this helps,
Nathan