Hi Irin
Could refer the links with steps
https://help.sap.com/saphelp_nw04/helpdata/en/69/c24c824ba111d189750000e8322d00/content.htm
Step by Step guide for client export import - Basis Corner - SCN Wiki
http://www.alternateplanet.net/2010/01/how-to-export-and-import-sap-users-and-authorizations/
Regards
Sriram