How to change surnames in title deed following marriage

Good morning. My wife and I purchased our property in 1999 before we were married (so both names on the registered owner section are "maiden names"). The charge by Nationwide was released in 2016, by which time we were married and both took a double-barreled surname from both maiden surnames. I have just downloaded the title and it still shows maiden surnames on the register. How would we go about changing the registered owner section with the correct surname? Is this a simple change or would the services of a solicitor be recommended? Look forward to your learned advice. Kind regards.