[Faiz Rafi]

i have an xperia sp that is running android 4.1.2 jelly bean. it was rooted but i already unroot it, but theres no software update button on the about opition in stting... how can this be???

[Rukbat]

That would have nothing to do with rooting - if all you did was copy a couple of files to the phone and install an app (which is what rooting is). If you ran a rooting program, who knows? It could have also removed that option. If by "rooting" you mean that you flashed a rooted ROM, that ROM may not have an update option.

We don't have enough information at this to do much more than give you possibilities. (And if you used a rooting program, only the developer who wrote it knows what it does.)