Thankfully, you can avoid installing this update on your iPhone by simply following simple steps that allows you to delete the current iOS software update on your iPhone..
Just as described by our friends at OSXDaily, you can delete the downloaded update by following these steps:
STEP 1: Go To Settings—–> General—–> Usage—-> Manage Storage.
STEP 2: Now you should see iOS 8.0.1 at the top of the list with size 1.1 GB, simply tap on it.
STEP 3: Tap “Delete Update” in order to remove the file from your iPhone.
This will effectively remove the downloaded update from your device and prevent you from accidentally installing it.