How do customers make changes to their bought website?

I am fairly new to making websites from scratch and selling them. As of right now, customers pay me a yearly subscription for me to keep updating their website. Every time a price or a text needs to be changed, they have to send me a mail including the small changes.

This often takes a long ting and I feel like I'm wasting my time and my customer's money. Is there a way for customers to be able to change simple stuff such as text, without needing any knowledge of how to code?

If not, is there a program that makes this process easier, so customers don't have to explain every single time a small text needs to be changed? Thanks!