How do I update iphotos to be compatible with mac os catalina

iPhoto cannot be updated any longer. The last update has been released in 2015 as compatibility update for OS X 10.10.3 Yosemite, when Apple released the successor to iPhoto, the Photos.app.

iPhoto cannot run on Catalina, because it needs 32bit frameworks, that are no longer provided the new system Catalina.

You can convert your iPhoto Libraries to Photos Libraries to have access to your photos on Catalina. That is described here: Updating from iPhoto to Photos for macOS – Apple Support

If you only had one iPhoto Library, it should be automatically migrated to Photos when you launch the Photos.app the first time. If you have more than one iPhoto Library or Photos does not find the library, hold down the options key ⌥ while launching Photos. Release the options key when the library chooser dialog appears and select the iPhoto Library you want to migrate.