==1. Verify disc image==

To get started, ensure you have an NTSC copy of Gran Turismo 4 Online Public Beta.
Use a file hashing tool to verify that the MD5 hash is 3306538778dda2ded87ceaf52c944a98. Other versions (such as the DNAS Bypass build commonly used to play online) are considered pre-modded and will not patch correctly if used.
If you're upgrading from a previous version of Spec II, check that the MD5 hash matches one of those listed in Step 3 and grab the appropriate .xdelta patch for your upgrade path.

==2. Extract Spec II .xdelta patch==

Extract the .xdelta patch containing the mod to a convenient location.

==3. Apply Spec II .xdelta patch==

Using either xdelta or xdelta UI, select your unmodified disc image from Step 1 as the input file, the .xdelta file as the patch, and select a name/path (e.g. Gran Turismo 4 Spec II.iso) for the output disc image.
Due to the size of the patch, this process may take a while and the window may appear unresponsive while patching. Once finished you will see a confirmation message. If you see an error message relating to invalid input, refer back to Step 1 and ensure you have the correct version of the game.
The output disc image should have a match one of the following MD5 hashes depending on your mod version - MD5 hashes can be checked here: https://www.theadmiester.co.uk/specii/changelog.html

NOTE: Some versions of xdelta may not preserve the .iso extension, meaning your patched disc image may not be recognised by your PS2/PCSX2 setup. Ensure that the output file has a .iso extension before continuing.

==4. Enjoy!==

You're now ready to start playing Spec II! Be sure to refer to the Frequently Asked Questions and Known Issues pages if you have any queries - these pages will be kept up to date with any new issues or FAQs.