In SharePoint 2010 the manage permission levels options by default do not appear on the screen. If we navigate to the manage permission page for a subsite it will appear as given below
Hence if we want to change or modify any permission level we will required to do so from parent site. This can be hacked using a very simple two line of powershell script.
$web = Get-SPWeb “<Sub site url on which the inheritance need to be broken>"
This two line of code need to be executed from the sharepoint WFE server. Once this is done user can see the below links on browser and free to do any changes on permission level for that sub site