How do I update my IPhoto to 64 bit?

You can't, there is no 64 bit version of iPhoto. iPhoto has been discontinued for several years. It was replaced by the Photos app.

You can open your iPhoto Library in Photos and continue to work with it. Photos is very similar to iPhoto.

See here: Updating from iPhoto to Photos for macOS - Apple Support

iPhoto was discontinued 5 years ago. It is no longer developed or sold. It was replaced by the more powerful (and free) Photos.app that comes with the OS. You can migrate to that app very simply:

Hold down the option (or alt) key and launch Photos. From the resulting menu select 'Choose Library' and point at your iPhoto Library. It will do the rest.

If you prefer not to use Photos there are several 3rd party apps that you can use. Which to choose depends on the kind of photographer you are and your budget.

You can't; all versions of iPhoto depend on a 32-bit library. Switch to Photos or a non-Apple alternative.

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