WeChat for iOS 7.0.13 is released today, allowing users to change their WeChat ID. WeChat for Android has previously supported changing the WeChat ID.
The WeChat team said on Weibo that WeChat for iOS now supports changing WeChat ID, users can update to 7.0.13 to experience it. The new feature is being covered gradually, you will have to try again later if it's not available yet.
If you want to change your WeChat ID, you can find "My" - "Personal Info" - "WeChat ID", and eligible users can change their WeChat IDs once a year.