How to increase your upload speed?

No, not really. In fact, the more upload you have, the faster you will send your packets to the opponent (e.g., you shoot at them, you send them packets).

Otherwise, accuracy has nothing to do with that.

Exactly i

1) To increase your upload => have a faster upload connection, like SDSL connections that are faster in upload than ADSL, or Orange's fiber optic with 100 Megas in upload.

2) Increasing your upload will not improve your gaming experience. On the contrary, you need to improve your ping! And for that, you must be lucky enough to be close to a telephone exchange.

3) There are tweaks to improve your game, like the frame rate in Counter-Strike...

In ADSL, the upload speed is limited... by law... 100kB/s in France...
Originally, the aim is to limit certain communication disturbances.

You need to change the protocol and switch to xDSL to have more upload (like VDSL...). Free has been offering this recently.