How to get MS Access to reach a Linked server on MSSQL
As Sean Lange mentioned, MS Access cannot use a linked server which is only accessible from within the SQL Server. But MS Access is external to SQL Server.

If you think of MS Access as the Client in a 2-tier Client/Server project, then it should be clear that you can use the 3-part naming convention (ServerName.Schema.Object) to access the SQL Server.  

If you have sufficient rights, you can update data in SQL Server from MS Access through the common use of T-SQL to manipulate SQL Server data.

If you want the SQL Server itself to fetch data from a MS Access database, then you could create a Linked Server in SQL Server that would reach out through a provider to get data from the MS Access.

https://msdn.microsoft.com/en-us/library/ms190479.aspx gives a sample provide setup from the Northwind database.

EXEC sp_addlinkedserver 
   @server = N'SEATTLE Payroll', 
   @srvproduct = N'',
   @provider = N'MSDASQL', 
   @datasrc = N'LocalServer';
GO