I need to update my iPhone

Assuming you have a compatible device, see: Update your iPhone, iPad, or iPod touch - Apple Support

And: If your iPhone, iPad, or iPod touch won't update - Apple Support

If the above Apple articles do not help, please post back with relevant information. 

sri ~ What model of iPhone is it?...

Settings > General > About > Model Name

And what version of iOS is it running?...

Settings > General > About > iOS Version

õ¿õ¬