All credit for this goes to slinkster213 at precentral, thanks for the amazing write up!

So I have decided to just take the time to properly list the details on EXACTLY how to properly remove your themes because I am tired of reading posts day after day about people having problems with either installing or removing their homebrew themes.
If you have a way of doing this other than what I have mentioned following please feel free to share so that others may share your knowledge.
Please stop posting thread after thread about questions related to this!!!

Installing with webOS Quick Install (WOSQI)
There are 2 ways of installing themes via wosqi and this assumes that you already have wosqi on your computer and properly setup. If you do not please follow the instructions on this thread
WebOS Quick Install


1. Install using a zip file

These files must be downloaded directly from the website PreCentral or PreThemer
You can find the themes in PreCentrals theme gallery here.
You can find themes in PreThemers gallery here
Click on any theme you would like to install
Scroll down the themes page to the section called "Download Options" for PreCentral Gallery
Scroll down to the large button "DOWNLOAD" on PreThemer Gallery. A new window will open and you will have the option to download a zip or a ipk. Download the zip.
Click on the link located in this section
You will be downloading a zip file. DO NOT DECOMPRESS THIS FILE ONCE DOWNLOADED. LEAVE AS A ZIP FILE
Remember where you downloaded the file
Now open WebOS Quick Installer
Select the "Tools" pulldown menu
Select "Themer" within this menu
Now a new window called "Theme Settings" opens up
Select "Load Theme"
A browser window opens up. Hope you remembered where you downloaded the zip
Select the zip file and press "Select"
Once you have selected the file another window called "Theme Info" opens up.
Here you will able to see the information of the theme that you uploading including screenshots, basic info on the creator and also a button called "Set Theme"
Push the "Set Theme" button if this is the theme you want to install
A window pops up saying "Changing Theme" DO NOT DISCONNECT the phone or touch anything. Wait for the theme to load and let it do its work
Once it has finished working another window will pop up saying "Theming Complete" Press OK.
This will restart Luna and the phone and will set the theme.
Your phone will reboot with the theme and YOU ARE DONE!!!

2. Install using an .ipk file

These files must be downloaded directly from the website PreThemer
You can find themes in PreThemers gallery here
Scroll down to the large button "DOWNLOAD" on PreThemer Gallery. A new window will open and you will have the option to download a zip or a ipk. Download the .ipk file.
Click on the link located in this section
You will be downloading an .ipk file.
Remember where you downloaded the file
Now open WebOS Quick Installer
In the main window select the large plus sign.
A browser window opens up. Hope you remembered where you downloaded the .ipk
Choose the .ipk file and press "Select"
Now that the file has been added to the queue window and your phone is connected via the usb cable. Press the large "Install!" button on the bottom of the window.
A popup window appears saying "Please wait..." So please wait and let wosqi do its thing.
The window will disappear and the phone will automatically restart. and YOU ARE DONE!!!


Uninstalling with WebOS Quick Install
This should ONLY be used with themes that are installed using wosqi. Do not use this for themes installed via Preware. This removes both zip files and .ipk files.

DO NOT INSTALL NEW THEMES OVER OTHER ONES. This will cause your phone to install themes over each other and files will be permanently changed. Some files may be changed and will not be changed to the default using this method. You wil have to us WebOS Doctor otherwise. And this sucks.

Follow the above directions to get back into wosqi and to the Themer area.
The "Theme Settings" window will now give you an option to "Revert to Default" Choose this option.
Again the "Changing Theme" window will open. Let the program do its thing and do not touch/disconnect the phone.
Once it has finished a "Theme removed" window will appear. Press "Ok" and let the phone restart.
Once it has restarted the theme will be completely removed and you are set.