The first thing you need to do is check out your repository to your local machine:
Then use your favourite editors to make changes. I suggest Notepad++ for text and Gimp for images.
Now to get those changes into the repository.
First set up the commit:
Then Sync it to make it happen:
If you use your browser to make a change to your repository, in your desktop appliaction you will see the sync button with a number by it, similar to the image above, but the arrow will be pointing the opposite direction. Click this and it will take the new changes and bring them down to your local copy.