Short Answer
If you are comfortable with you skills and knowledge of WordPress, you should update your website yourself.
Long Answer
Modern websites are much more advanced than the websites of a decade ago. Websites are no longer a “set it and forget it” online solution for your business. A business’s website is the face of the business on the internet, and website owners should take as much, if not more, care of their website as with the business where their physical office or store is located. A website should be treated as being as important as the business itself. 80+% of Americans do an internet search to get information about a business before they ever call or go by a physical location. This means the website is very important to the success of a business.
To put it simply, businesses should at very least treat their website as a utility for their business, paying for regular service. Regular WordPress maintenance ensures the business’s website is online, free of malware, and running smoothly.
Websites that are out-of-date are susceptible to hackers, broken forms, broken layouts, broken links, slow speeds, and more. The cost a losing a single customer due to a broken website, would likely pay for the cost of monthly maintenance service.
The benefits of having a professional keep the WordPress website up to date is more than worth the low monthly fee.