[thegrube]

I get my wife's hand me downs. She has the new iPhone 6 and I got her old iPhone 4 with iOS 7.1.2. She has over 500 old messages on the phone I got. Is there a freeware software program that will delete these all at once? I know there are many versions of data clean software that have free trials but the free trial versions won't delete these.
Thanks

[natasftw]

Top left corner of message app. Hit "Edit" Check each box. Bottom right, hit "delete"

This requires less effort than you've already spent trying to find an alternate way to do the same task.

[Just_Me_D]

Alternatively, you can go to Settings - General - Reset, and then select "Erase All Contents and Settings". This will give you a clean slate, so to speak.

[Ledsteplin]

Messages app? Long press on a speech bubble. Tap "More". Then tap "Delete all" in upper left corner. Then tap "Delete conversation".
Or just delete each thread on the menu.