When you install Mint, it'll deal with deleting windows on its own.

Installing it will be broken down mostly into:

• download the right version of Mint.
• make a USB to install ( it's not just putting the file onto the USB)
• plug the USB into your old laptop, turn the laptop on, then follow the steps.

A much better guide (with pictures!) is https://linuxmint-installation-guide.readthedocs.io/en/latest/