Hi Krishna,
From any Transaction, use menupath System> Status... The click on the "magnifying glass" icon just below the "Component Version" field - that will open another dialog screen with the Support Package Level for Installed Software Components.
Find the entry for component SLL-LEG - that's the GTS system. Up to 8, the versioning is quite obvious, but release 900 is actually GTS 10.0, and 901 is GTS 10.1.
Hope that works ok for you.
Regards,
Dave