When your iPhone or one of its applications malfunctions, a crash report is generated and stored on your device – typically as a CRASH, PLIST or LOG file. Because these reports are relatively small and replaced by new crash logs every few days, you needn't worry about the space or resources they consume on your device. That said, an iTunes sync can wipe crash reports from your device and copy them to your computer for future reference. It's more important to periodically purge the iPhone crash logs that you accumulate on your computer because collectively they can grow considerably over time.

Remove Crash Logs from iPhone
Step
Tap "Settings" on your iPhone, followed by "General." Next, choose "About," followed by "Diagnostics & Usage" and "Diagnostic & Usage Data." Observe the list of crash, usage and diagnostic reports logged on your device. If you wish to review the detail of an individual item, tap it.
Step
Launch iTunes on your computer. Next, connect your iPhone using its supplied USB cable. Choose your iPhone's name under Devices in the left sidebar.
Video of the Day
Step
Click "Sync" in the lower right corner of your desktop's screen. The sync process begins and advances through several steps. You can check its progress in the area above the main pane's navigation bar.
Step
Return to Diagnostics & Usage Data screen on your iPhone. You'll see that most, if not all, the previously logged items no longer appear, having been copied to your computer and erased from your device during the sync.
Erase Crash Logs from a PC
Step
Open File Explorer on your computer. Type "%APPDATA%" in the address bar and then press "Enter."
Step
Navigate to Apple Computer\Logs\CrashReporter\MobileDevice\YourIPhoneName. A list of previously synced crash log files display.
Step
Position your cursor within the file directory and press "Ctrl-A" to select all files. Alternatively, Ctrl-click select files only, then press "Delete" to erase the files.