Go to www.limewire.com and download and install the newest version.
If what you're afraid of is losing all your previous files with the update, then fear not.
If it's an upgrade you want (upgrading=going Pro) then follow the links in the LW site. Same thing about previous files also applies to Pro

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iMac G4 OSX 10.3.9
RAM 256MB
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps

"Raise your can of Beer on high
And seal your fate forever
Our best years have passed us by
The Golden Age Of Leather"
-Blue Öyster Cult-