First things first, click the Apple logo and open System Preferences.
Next, click "Software Update." Both updates and upgrades can be found in the same place!
The most recent available upgrade will appear. When it's done searching for upgrades, click "Upgrade Now."
Remember, you are downloading new software, not updating the software you currently have. So, it takes time for your computer to download the new MacOS from Apple's servers.
There are many factors that determine download speeds, including your internet connection, anywhere from 30 minutes to 2 hours can be reasonably expected (my download took 58 minutes).
Either way, allow your Mac to do its job and complete the download. Walk away and avoid using your computer during this time.
Once the download has completed, you will see a pop-up that shows you the MacOS name and asks you to click "Continue." Click "Continue" to move to the next step.
Next, agree to Apple's terms and conditions.
Click your hard drive, which should be "Macintosh HD" unless you have renamed it, and click "Continue."
Depending on your Privacy and FileVault settings, you will be asked to enter your user password and/or Apple ID password. Sometimes, you may have to enter both. Enter the password, and click "Unlock."
Now, simply allow your Mac to install the update.
This step may take up to 2 hours to complete. Again, this is another step where you can allow your Mac to complete the steps. Walk away, get a cup of coffee, and check on your Mac's progress a little later.
You will then be prompted to update your Mac. Click "Restart," allow your Mac to reboot, and celebrate a successful MacOS upgrade!
Once your Mac reboots, you will be required to sign in and may be prompted to follow some additional steps. If you aren't, you are good to go enjoy the rest of your day! If you are prompted with additional steps, continue with this guide.
Depending on the MacOS version you upgraded from and to, you may be asked to set up FileVault. Whether you set up FileVault or not is really up to you.
That decision should be based on how often other people have access to your Mac, what kind of private information is stored on your Mac, and how much security you believe you need. If you decide to turn on FileVault, check the box next to "Turn on FileVault disk encryption." If you do use FileVault, I strongly suggest clicking the second box that allows you to use your Apple ID to unlock your disk in the event that you forget your password for FileVault.
Either way, when you are done, click "Continue."
Depending on the MacOS and your current iCloud settings, you may also be prompted to decide if you would like to store your files on iCloud. For those who have the iCloud storage, this is a good precaution for future data loss.
Once you've decided, click "Continue."
Lastly, you may be prompted to sign in with your Apple ID and password. Once you are done, allow iCloud to set up your account, and voilà!
Now, you have upgraded and set up your Mac to the most recent version of MacOS!