Unable to update AT&T Galaxy S5 to Lollipop on stock Touchwiz

I have an AT&T Galaxy S5 that has the default version of Touchwiz on it, with Android 4.4.2. I never rooted or flashed any roms on this device, yet I am unable to get OTA updates. My friend, who has the same phone with AT&T, updated to Lollipop a while ago, and recently got another update, both of which I didn't get. What can I do to update my device to Lollipop?

Thanks,
Sid