FIRST GO TO https://www.microsoft.com/en-in/software-download/windows10startfresh .
Then click on download .
Then the download will start.
Then after downloaded Click on continue instalation .
Then the pc will restart.
So you can get windows 10 in windows 7.
But,sometimes the download may fail and the pc may not work.
If you downloaded in windows 7 update it to 8 or 8.1 .
If you directly update to windows 10 in windows 7 the pc may run slowly