DISCLAIMER...
This will erase everything on your phone.
You may brick your phone. However, I have done this stuff tons of times and have not had any issues...
1st thing you need is the drivers for your computer, I am sure you can find them in one of these threads...
Install the drivers.
Download all the files from dropbox.
Open odin
Make sure one package is checked.
Click the OPS button and chose the .ops file you downloaded.
Click One Package and choose the CWM file.
Now put your phone into download mode... Power off the phone. Then hold space + p while powering on. The phone should say "downloading..." in yellow..
Connect to the phone to your computer via USB. FYI the phone will not enter download mode with USB connected...
One of the boxes in odin should turn yellow.
Click Start in odin.
Quickly press and hold "U" on phone keyboard.
It should reboot into clockwork mod recovery.
Use CWM to make a backup, this way if anything should go wrong you can get back to where you started.
Then from the CWM menu - reboot.
Ok, now that you have a backup, do the process again, but put the EK18.tar file in the one package section instead of CWM, hit start then just let it work its magic (don't hold down "u") it will reboot (it may take a few minutes, just be patient) and you should have it.
Edit: FYI EK18 is for SPRINT