This file is in SVG format. That means you can edit it with a text editor or an SVG-compatible graphics editor. However, you will find it better to use a text editor because otherwise your edits will be too imprecise.

Updated image is available from http://postimg.org/image/4p275r9g1/. Whoever has uploads rights to wikimedia - please replace the current version with it. The 2011.5+ data is taken from http://en.wikipedia.org/wiki/Usage_share_of_web_browsers (Wikimedia section).

If the data is between 1996 and 2010, just find that point in the file and update it. For example, at the moment the code for the usage statistics between 2000 and 2001 looks like this:

L 2000,83.75
L 2001,90

To insert data for the midpoint of 2000, just make it look like this:

L 2000,83.75
L 2000.5,86
L 2001,90

If you are adding data for before 1996 or after 2010, you'll need to change the transformations on the groups. This requires moderately detailed understanding of SVG. Seek help if you need it.

The original graph is at Internet Explorer usage share.png. That is the original source of the data. The data at the time of this SVG's creation was:

"Date","Percentage"
1996,3.75
1997,17.5
1998,35
1999,62.5
2000,83.75
2001,90
2002,95.25
2003,94.75
2004,92.625
2005,86.903861
2006,1

El T at English Wikipedia