You can or i can
Nearly all the sites I make are built with WordPress, which is software that allows you to log in and update and add things yourself.
It’s very user friendly, but I still do a lot site updates for my clients. Adding blog posts. Changing text. Anything. Often they decide it’s more efficient to pay me to do it rather than do it themselves, it gives them more time to focus on their main business activities.
I can update your site for you even if someone else designed it, I might be cheaper than they are? (I’m $60/hr, charged by the minute, and I’m fast.)