How to remove the code from your theme
If for any reason, 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. To learn how to do the latter, follow these easy 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.