SELECT is_read_committed_snapshot_on, 
       snapshot_isolation_state_desc, 
       snapshot_isolation_state 
FROM sys.databases
WHERE name = '<dbname>'

ALTER DATABASE <database> SET SINGLE_USER WITH ROLLBACK IMMEDIATE ;
ALTER DATABASE <database> SET allow_snapshot_isolation ON;
ALTER DATABASE <database> SET READ_COMMITTED_SNAPSHOT ON;
ALTER DATABASE <database> SET MULTI_USER;

SELECT CASE transaction_isolation_level
WHEN 0 THEN 'Unspecified'
WHEN 1 THEN 'ReadUncommitted'
WHEN 2 THEN 'ReadCommitted'
WHEN 3 THEN 'Repeatable'
WHEN 4 THEN 'Serializable'
WHEN 5 THEN 'Snapshot' END AS TRANSACTION_ISOLATION_LEVEL
FROM sys.dm_exec_sessions
where session_id = @@SPI