When you learn lesson no 1 in life nothing is free then you will be well ahead of most other people.
Why do you think 6m is slow. What are you doing that is using 6m. If for example you are watching youtube and it uses 1m which leave 5m if you were to upgrade it will still only use 1m and now would just leave 7m unused. The only way increasing your bandwidth will help is if you are using it all already. I would look at the performance monitor in windows 7 or vista. It will give you a basic indication of how network bandwidth you are using. There are a number of other tools you can load to your pc. Now this is only for YOUR pc if there are other devices using the same router it will be a little harder to determine how much...