The downloading of updates in Windows Server Update Services (WSUS) is based on Background Intelligent Transfer Service (BITS). BITS is designed to download big files using idle bandwidth only. If you need to speed up the downloading process, you may change it to use a foreground mode.
To do that, you need a SQL Management Studio to connect the database used by WSUS. The database name is SUSDB. You can run this command in that database specified:
update susdb.dbo.tbConfigurationC set BitsDownloadPriorityForeground=1
For reversion, run it again with replacing the 1 to 0.