I use imac g5 and need to upgrade my itunes to 7.5.5 or later

There is no iTunes 7.5.5. If you mean iTunes 10.6.3, click here. If you want to update QuickTime, click here.

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The maximum iTunes version is 9.2.1 for a G4 or G5 running Mac OS X 10.4.11, 10.6.3 for a Mac running 10.5.8, and 11 for computers running Mac OS X 10.6.8 or above. - https://discussions.apple.com/thread/5683895?answerId=24186956022#24186956022

iTunes 8.2.1 - http://support.apple.com/downloads/iTunes_8_2_1

iTunes 9.1.1 download - http://support.apple.com/kb/DL1036

iTunes 9.2.1 - http://support.apple.com/kb/DL1056

iTunes 10.6.3.25 - http://support.apple.com/kb/DL1575