First of All... here is a link to Oracle Documentation for tablespace management commands/syntaxes. It will guide you on how to manage tablespace with command.ALTER TABLESPACE http://docs.oracle.com/cd/B28359_01/server.111/b28286/statements_3002.htm
Alternatively, if you have Enterprise Manager access, you can do it with GUI. It will also generate/show the command to perform the operation which you can use for further similar operation.
And the last... it's a SQL Server forum and we (usually) don't discuss Oracle issue here. There are couple of good Oracle forums where you can seek for more information specific to Oracle. Also, in SQL Server Central, we have a forum 'Working with Oracle' where we discuss the issue that are related to Oracle (in connection to SQL Server, like linked server). Many experts who have experience in Oracle & SQL Server post there, you can utilize it as well.