Hi, You are using a Mac so here you go.
1. Open up Lightroom on the computer that has all your presets.
2. Press the [CMD] then [ , ] key on your keyboard - this will open a window titled "Preferences"
3. In the Preferences window, locate and click the Presets tab, then click "Show Lightroom Presets Folder"
4. Locate the Develop Presets folder and in that folder you should see all your presets
You can copy all your presets and load them on your new computer > in Lightroom > in the Develop Presets folder. You can find that folder by following the steps 1-4. Hope that helps!