Why Can’t I Change My Profile Picture?

If you are QQ level 4 and below, you can only customize your profile picture once. However, you have the option to change it within 72 hours however many times.

But once that 72-hour grace time period passes, you can not change it again unless you become a QQ VIP member or reach QQ level 5 – that is 32 active days of usare (Details on how QQ levels are calculated)