On my home and office computer, the update tab was missing in my Sun Java 1.6 Control Panel applet. At the office, I found it was disabled in the registry.
Steps to find it*:
1. Start, Run, type regedit, OK
2. HKEY_LOCAL_MACHINE > SOFTWARE > JavaSoft > Java Update > Policy
3. I have a DWORD value titled “EnableJavaUpdate” with the value of “0” (zero). I changed it to “1” (one) and the update tab appeared.
At home, this registry entry wasn’t there. I could have tried adding it, but instead, I went to JAVA.com and installed the latest version, which added the update tab.
*Be very careful; messing with the registry can be very risky.
If this doesn’t work, check out jjoensuu’s and roja’s comments below.