SW for Devs - Updating A Game
To update a game you've already uploaded, login in the SW for Devs application and then select the "Update A Game" tab on the left.

The Fields explained

Game Name - Select the game you wish to update. If it's the name itself you wish to update, file a ticket.

New Description - Only enter a new one if you wish to update the old one.

New Instructions - Only enter new ones if you wish to update the old ones.

New Category - Select your game's genre. If none fits, go with the "Other" option.

New Width and New Height - Only enter width and height if you wish to change the old ones.

New Game File - Upload your new game file. Two things to consider here:

I. Your file must not exceed 15MB and
II. If you're uploading a HTML5 game, the index.html of your game must be in the root of your .zip file, not within any folders - otherwise you'll get an error on your game's page.

Image/Thumbnail - An image of your game

After you've filled them all out, make sure to check the 2 boxes below and then hit "Update Game"! It may take a while to get redirected to the game's page depending how big your game's file is.