If you have a Lion installer on a USB thumbdrive, you can use it to upgrade your Mac from Snow Leopard to Lion, but if you have an older version of OS X you can’t upgrade. You need to first upgrade to Snow Leopard OR you can erase everything and do a completely fresh install of Lion. After installing Lion on my iMac, I wanted to delete everything on my laptop and do a fresh install of Lion. But the installer will not install over an older version of OSX. I had to delete the old version of OSX, then install Lion from the USB thumbdrive. Here’s how to do a fresh install of Lion.
Here are three different ways to put Lion on a USB thumb drive. If you buy and install Lion from the App Store it downloads all 3Gigabytes from the App Store, installs Lion, then deletes the installer! So when you go to install it on another machine it needs another 3Gigabyte download! Here’s how to make a re-usable installer.
The new OSX Lion comes as an upgrade from the Apple App Store – not on a DVD. The good news is that once you’ve paid for it once, Apple allow you to install it on all the computers you own for free! After you purchase it from the App Store you just have to go into the App Store on your other computers and Lion will be there – all paid for and ready to download again!
The Apple page on this is here.
Of course, you need to upgrade all your existing computers to Snow-Leopard first.
The main hitch is that it needs to download lots of files first.
You can make a USB installer and copy it across manually. Here is a way to do this using the built-in Disk Utility in OS X.
It took me a while to get my canon scanner working under Lion. The trick is that there are two programs that you need to install – the scanner program and the driver. This works for Leopard and Snow Leopard too.