If you want to do an offline update from VS17.12 to 17.13 , you can follow below steps:

1. Update the layout to a specific version of the product.

• Go to the Visual Studio 2022 Release History page and download a particular fixed version bootstrapper(e.g vs_Enterprise17.13.0), copy it into your layout, and use it to update the layout to that exact version specified in the bootstrapper.
• Run the --layout command in an elevated prompt to download the latest packages into your layout.

vs_enterprise.exe --layout c:\VSLayout

2. Update your Visual Studio 2022 by running the Visual Studio Installer > Update or you can also use the following command:

vs_enterprise.exe update --noWeb --quiet --installpath "C:\Program Files\Microsoft Visual Studio\2022\Enterprise"

Update

The easiest and fastest way to update your offline Visual Studio instances: using a minimal offline layout.

Do i have to download the entire VS Layout package everytime if there is an version update?

Unlike a full Visual Studio layout, a minimal layout only contains the updated packages, so it is always smaller and faster to generate and deploy.

1.Generating a minimal layout.

MinimalLayout.exe generate --targetLocation c:\VSLayout\ --productIds Microsoft.VisualStudio.Product.Enterprise --baseVersion 17.12.5 --targetVersion 17.13.0  --languages en-US

2.Update the Visual Studio Installer

vs_enterprise.exe --quiet --update --offline C:\VSLayout\vs_installer.opc

3.Update the Visual Studio application

vs_enterprise.exe update --noWeb --quiet --installpath "C:\Program Files\Microsoft Visual Studio\2022\Enterprise"

Docs Referred:

Update the layout to a specific version of the product

Update Visual Studio from a layout