Using Mission Planner
Connect your aircraft to the ground station computer using a micro USB cable
Launch the Mission Planner Program
Selecting the “Data” icon at the top of the window to open the Mission Planner Flight Data screen
Select the “DataFlash Logs” tab on the lower left pane of the window
Click the “Download DataFlash Log Via Mavlink” button
Select the log(s) you want to download from the left pane of the popup window
Click “Download Selected Logs”
Wait for the log files to download
This will save the selected log(s) to your MissionPlanner/logs directory, in a folder named after the vehicle type, such as OCTOCOPTER.