how to restrict ftp user to a directory?

can anyone please tell me how to restrict an ftp user to a specific directory ? for example, I want user1 to /home/www/user1 , and user2 to /home/www/user2 , so they can't go to /home/www or /home ?

and which command to let them upload/download ?
I'm using vsFTP server.

 

 

 

 

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