You can install this module directly from your backoffice Addons Marketplace manager, or even download the .zip package from the PrestaShop addons site, and upload in that way. Both methods are working, so you can dedice which one is more comfortable for you.
Use the built-in Addons Marketplace
You need to click on the Improve/Modules menu item of your PrestaShop dashboard, and login with your addons account. Then search for 'LayerSlider' term there, or click on the Categories filter button, and select Design & Navigation. Now the LayerSlider appear in that view, so click to purchase or if you done it previously then just click on the install button.
Install the LayerSlider in Addons manager step 1
If everything is OK, then you will see a confirmation message.
Install the LayerSlider in Addons manager step 2
Install with the .zip package
This way is also working, if you download the installation .zip package from the PrestaShop addons page. Just click on the Upload Module button, and browse the installation package, or simply drop that from the file manager.
If you got error or warning messages during the installation, you should make sure that the extension working properly, or not. If you experienced a malfunction in the module manager, please contact us on the PrestaShop Addons page.