Adobe Illustrator is the industry standard computer program for creating vector graphics. Unlike raster graphics similar to those created by Adobe Photoshop, vector graphics can be scaled to any size and maintain their original quality. AI is the file extension used by Illustrator, and while some older versions can be opened in other programs, the best thing to do is open the file in Illustrator and edit it there. Even with no experience, there are several simple operations you can do with little help.
Open Illustrator and set up the workspace. Clicking on the Window menu allows you to open the palettes you want to always show. At a minimum, have the Color and Swatches palette open. If you are working with a large amount of text, open the Character and Paragraph palettes. Make sure your toolbar is visible as well. Any changes you make here without a file open becomes the new default.
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Open the file and click on the various parts with the white arrow. This shows you the various parts of the graphic, allowing you to see how it is set up.
With the proper part of the graphic selected, look at the color toolbar and see what color the graphic is. On the color toolbar, there are two options for viewing color. The square with the "hole" in it shows you the color of the outline or stroke, while the solid square shows you the fill. Use the swatches palette to change colors as needed, and the Stroke palette to eliminate the outline altogether.
Select the pen tool and add or delete anchor points. You can also change the curve from rounded to square if needed.
Save your changes. If you want to edit the graphic in another program, save it as an eps or svg file.