Q: my mac says photo 11 is available for update, but when i click update it tells me i have to sign into account i used to purchase it , please help

Welcome to the Apple Support Communities

If you purchased iPhoto from the App Store or it came with your Mac, first see > http://support.apple.com/kb/TS4236 If it doesn't work, maybe iPhoto is hidden, so you have to unhide it > http://support.apple.com/kb/ht4928 Finally, try to update it.

If you have a second-hand Mac, you can't update iPhoto because it's registered to the Apple ID of the first owner. In this case, the only solution is to buy iLife '11 on a DVD and install it from there

Have you gone to the App Store app in the Apps folder, signed into your account, opened the Purchases pane and accepted the iLife apps into your account? You cannot update the preinstalled iLife apps until you have done so, Depending on how long that you have had the Mac, it may be too late to do so. At which point you woud need to wipe the Mac and start over.