Replacing PCIe power cables on a power supply

Hello,

I am having GPU issues. Computer tech told me GPU was on fritz GTX570) so I replaced with an AMD 7570. That initially worked fine but now failing to run games and occasionally to post. The computers bulder suggests it may be a power supply issue and is going to send me new PCIe power leads. That's fine but how do I change them on a Thermaltake Litepower 700?

Best,

Graham