I have iPhone6 128GB but when I made software update it's showing 114GB please advise urgently

128 GB is the available space on your phone. If you install all the default firmware, this space reduced to a smaller usable part.

My 64GB, for example has only 56GB usable space with no other software installed than the one that came with the phone.

Plus, the capacity of a hard drive is calculated differently if it comes to computing and selling.

In my case: 64GB advertised * 0,93 computed size = 59,5GB available size, minus the firmware size 2GB, makes 56 GB usable space.

Take it up with Apple at http://www.apple.com/feedback/iphone.html

128GB*0,93=119GB available, minus firmware size for iPhone 6, which I don't know exactly, your 114GB seem to be ok.

Apple hardly ever replies back to post to their feedback site.