Change database to single user mode as shown in the other answers
Sometimes, even after converting to single user mode, the only connection allowed to the database may be in use.
To close a connection even after converting to single user mode try:
select * from master.sys.sysprocesses
where spid>50 -- don't want system sessions
and dbid = DB_ID('BOSEVIKRAM')
Look at the results and see the ID of the connection to the database in question.
Then use the command below to close this connection (there should only be one since the database is now in single user mode)
KILL connection_ID
Replace connection_id with the ID in the results of the 1st query