How to remove the code from your theme
If you need to uninstall the app, you can do so by deleting it from your Shopify admin or by removing its code from your theme code files. To learn how to do the latter, follow these informal steps:
1. In your Shopify admin, click Online Store and go to Themes.
2. Click the Actions drop-down menu and choose Edit code.
3. Go to theme.liquid.
4. Scroll down to locate the page speed optimizer file as shown below and delete it.
5. Click Save.