As for the link, scroll down and hit Download:

x0ry14
It works as a free download, tested.

As the existing SD card in the unit is only 2GB with European maps on it. Would I now need another SD card about to download the 17.5 GB onto.
Keep the old sd as a backup and use a new one formatted FAT32, the rar contains 2 PDF, instruction and old Fastactivate for TT maps, so unpack to check the right size of the needed sd.
If it works, you can find recent Fastactivate and new maps in TT section.

Can you just explain how I would change any new SD card from SDHC to Fat32 please?
SDHC cards are another type of sd:
Code:
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your unit doesn't recognize them.

FAT32: is a formatting method for storage hard drives:
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You can simply Google these terms to understand stuffs, Google is your friend
Windows can format your new sd as FAT32.

Do I just insert the new SD card in the unit and as you say press reset and wait?
Sorry I don't have your unit, all the info I got I found in the net, read instructions included in rar from the link I posted.