To follow these instructions you will need to jailbroken. You can find instructions on how to jailbreak your device here.
Launch Cydia from your Springboard.
Press to select the Sections tab at the bottom of the screen.
Press to choose Tweaks from the list of sections.
Press to select Safari Upload Enabler from the list of packages.
Press the Purchase button at the top right of the screen to buy the tweak for $1.99. Press the Install button that appears once your payment has been authorized.
Press the Confirm button to begin installation.
Once your installation has completed successfully press the large Reboot Device button to restart your device.
Once your device has rebooted, press to launch Safari from your SpringBoard.
Navigate to a web page with an HTML file upload field and press the Choose File button.
Safari Upload Enabler will now show you a directory listing of files on your device that you can select from for upload. You can also select an image from your Photo Library.