Prime Minister Kevin Rudd says any changes to the pension system may have to wait until the completion of a comprehensive review of Australia's tax system.The review is being undertaken by the Treasury Secretary, Dr Ken Henry, who will release a discussion paper by the end of July and provide a final report to government by the end of 2009.Speaking to reporters in Brisbane today, Mr Rudd said he understood it was difficult to make ends meet on the pension."I understand full well that people on the age pension are finding it very difficult, that's why we need to have a complete, all-round look at this through the Henry commission of inquiry," Mr Rudd said."It's very important to make sure we have a thorough, long-term response to the long-term challenges of retirement income policy and that means for pensioners, it means for carers and it means for others." AAP