how do i replace ds lite housing? please urgent help required?

please help housing in ds lite broke so i bought the housing on ebay its perfect but i thought that there would be no problem in replacing it oh was i wrong she wants santa to bring her it as her surprise the housing arrived yesterday i also have another ds lite that my friend`was throwing it away so i took it the bottom screen is broken but i bought that too on ebay replaced the screen but i broke the power switch lol should have left it alone
please any help is welcome
thanking you