I can't upload program on my Arduino Mega 2560

Hi,

I recently have bought an Arduino mega 2560, and when I connect it to my computer (windows 10), the Arduino ide can't upload program on it!
When I click on the upload button, after a long time, it says :

avrdude: ser_open(): can't open device "\\.\COM7": Refused access


Problem uploading to board.  See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.

I have no idea why.

Thank you for helping and sorry for my bad English