My IMac mid 2007 has 20 gigs remaining on hard drive.What should I do?

First let’s make sure your computer doesn’t have some potential empty space hidden;

1. Lots of people put items in the trash but don’t empty the trash. I don’t mean to sound insulting but, make sure you go up to the Finder menu and select empty trash.
2. If you use iPhoto or Aperture launch them, right click on the trash can, and select empty trash. (I’m a long time user of the Mac and I’d been using iPhoto for 2 or 3 years before I found out the trash can kept everything until it was emptied)
3. restart your computer and hold the shift key until the Apple icon appears. This is safe mode and one of things booting into safe node does is to trim and erase temporary files that might not have gotten properly erased or trimmed. Once you get to the desktop restart normally.

This may have recovered almost nothing but at work I’ve seen these 3 steps make full drives suddenly nearly empty again.

So, you really do need to free up space. The thing to keep in mind is that word processing files, desktop pictures, etc don’t take up much space. To free up serious space you need to remove media - video, songs (albums of songs, not just one or two), and digital photos. If you are using iPhoto or Aperture you can move the their library that’s in your Pictures folder to an external drive. After doing so trash it (and empty the trash) then double click on the library you moved to the external drive and your program will launch and now know where to find the library. Read this Apple article to learn how to move iTunes to an external drive.

Rslep wrote:

How do I get the pictures into an Aperture Library? I have the same problem with IPhoto. I have moved, but not yet deleted the photos from IPhoto. Once I complete this operation, I will have lots of room on my hard disk.

I don’t have an Aperture folder, it is a package. You may have to start Aperture while holding the option key and then select the Aperture folder. Or maybe even re-import the pictures.

Upgrade. I purchased a 1T HD from Otherworld computing online for $57.00, used their videos on YouTube. The HD I'd hard to get out & back in because room is limited, but taking apart the iMac is easy. Fixit also has videos on YouTube, I found it very helpful. It's also good to know if you let your AppleCare expire like I did. Make sure you buy the tools to fix your Mac.