The first requirement is that your background is of one consistent color. With that being the case, you can use many different graphics software that have transparency tools for removing background color.
However, there are a few caveats: The file must be saved as a gif, png, or tif file (gif is most common, but png allows less dithering, more colors, and multiple transparencies,). If the logo merges into the background (e.g., a red logo has edges that melt into the white background by progressively lightening from red through light red to white), you may not have a sharp edge to your logo using a transparency tool, in which case you may have to resort to removing pixels around the edges one by one. This pixel editing may also be necessary if your background is not a solid color or of different colors.
Once you're background is transparent, you can upload to Emma and add it to the document.
I'm sure there is much more that can be said, but I'll leave that to others. Hope this helps.