How do you upload sim into game from exchange??

You'll need to start a new game to use them. Unfortunately, it will be in a different town so you won't see your old sims there.

you go into the game press ctrl+alt+c type "testingcheatsenabled true" then click shift and at the same time click on your sim then click edit in create a sim.

Click download on the Exchange (can only do with an account) and open the launcher. Anything you download then has to be installed on the Launcher. Open the TS3 Launcher and click "Downloads" then find the icons for the stuff you downloaded. Sometimes it will happen automatically, but most of the time you'll have to press "Install". Once the item has finished installing, enter the game as usual and any custom content will now be available to use on Sims. If you downloaded an entire family, just go into a saved game, click Edit Town from the ellipsis menu (options), and then you can add the new household, just as you can add new lots you may have also downloaded. If you want to stay in the same game as another household, you can just change the active family and play as the downloaded family in that game file, or you can start a new game and just select that family from the family bin and move them in.