How do you upgrade to Mac OS X 10.7 "Lion" from Mac OS X 10.6 "Snow Leopard"? Is it possible to upgrade from older versions of Mac OS X?

Apple's official instructions to upgrade to OS X Lion from OS X Snow Leopard are quite simple and involve only three steps -- amounting to little more than "make sure your Mac can run Lion, make sure you have the latest version of Snow Leopard, and download OS X Lion from the Mac App Store."

Best case scenario, those instructions are sufficient, and you definitely will need to verify that your Mac is compatible with OS X Lion, that it has at least 2 GB of RAM, and that it has been updated to Mac OS X 10.6.6 "Snow Leopard" or higher (10.6.8 is recommended).

However, before you even get to those three steps you absolutely should do the following:

• Backup absolutely everything. It's always a good idea to "clone" the entire hard drive to an external drive using Carbon Copy Cloner or SuperDuper and make a second backup of individual files that are particularly important. It's not a bad idea to make two full backups of the hard drive should you have the budget to do so.
• Verify that the backups were successful. This step is extremely important!
• Check to make sure that all of your software is compatible with OS X Lion. No PowerPC Mac OS X applications will work with OS X Lion -- even those that would work just fine with Snow Leopard -- and this software will need to be updated or replaced. Those with expensive applications may wish to delay upgrading to allow more time to purchase new software.
• If you are running a Mac for "mission critical" purposes, it always is wise to wait until others have experimented with OS X Lion on their Macs and a couple of bug fixes have been released (as of the date published, Apple has released one bug fix, 10.7.1, and a second one is on its way).

After making at least one backup of your hard drive, verifying the the backups were successful, checking to make sure that your software is compatible and/or you have the funds to upgrade or replace incompatible applications, and accessing your willingness to use your computer to essentially test a new operating system, then you are ready to proceed with Apple's official instructions.

Officially, you cannot upgrade a Mac running Mac OS X 10.5 "Leopard" directly to Mac OS X Lion, but MacWorld has provided a clever unofficial method of doing so.

Site sponsor Other World Computing sells a wide variety of external hard drives for backups.

Also see: What are the "pros and cons" of upgrading to Mac OS X 10.7 "Lion"? Is it worth it? What are the best reasons to upgrade? Are there reasons not to upgrade?