Q: How to switch from old iMac iMac (24-inch Mid 2007) to new one

You’ll be given the option to do so when setting up the new iMac; it can work through a network, an external drive, or Target Disk mode.

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Here's a link to an Apple support page on the Migration Assistant:

Move your content to a new Mac - Apple Support

That is the easiest way to move content to a new computer. Be sure though that any application you move from an old operating system to the new Mac are compatible with the operating system on the new Mac.