If you registered your WeChat account using a non-China's mainland mobile number, email address, or via Facebook Connect and have not linked your account to a mobile number with the China's mainland country code (+86), you are currently a WeChat user.
How to Switch to Weixin
To switch to a Weixin account, you must link your WeChat account to a Chinese mainland mobile number. Here’s how to do it:
Go to 「Me」>「Settings」>「Account Security」>「Phone」> Change Mobile Number.
Bind a China's mainland mobile number to your account.
Learn More
To understand the difference between a WeChat user and a Weixin user, visit:
My Account > WeChat and Weixin > “What is the difference between a WeChat user and a Weixin user?”