Hi,

I bought a new deck and two new blades for my Craftsman 16 hp, 42 inch deck, garden tractor. I would like to know the procedure for taking off the old deck and putting on the new one.

Thanks for your help

If you don't have the manual, it's here online
http://www.hammerwall.com/Download_Manual/37543/
I don't have personal experience with this mower, but I am sure that it is like most other riding mowers. What you want to do is to lower the deck all the way to the ground, or as far as it will go. This will allow for better access. Next, you want to look for the supports the mower deck, i.e. anything that looks like an arm that is attached to the deck. You may have to pull pins out as well.
After this, you should be able to pull the deck straight out from under it.
Here is a link to a video of how to pull the deck out. I know it isn't your type, but it should give you the gist of it.
http://www.hammerwall.com/Download_Manual/37543/
Note: you will want to remember where to put everything back after you take it out.