dbo is the default schema in SQL Server. You can create your own schemas to allow you to better manage your object namespace.
Actually you should leave those dbo. statements because your SQL will be faster since the optimizer doesn't have to lookup the schema. You can get more info here: Performance
Impact of Procedure Calls without Owner Qualification
In SQL Server, you could have several schemas (the "dbo." thingie) with the same table name, e.g. dbo.MyTable, joe.MyTable, frank.MyTable.
If you then issue a SELECT (list of fields) FROM MyTable, SQL Server has to first figure out which of the "MyTable" tables you really mean --> this costs time, specifying right off the bat you want "dbo.MyTable" will SAVE you time.
OK, not a lot on a single query - but SELECT queries are QUITE frequent and it all adds up!
You can change a table in SQL Server that starts with a dbo prefix to one without. To do this, you can do the following:
IF (NOT EXISTS (SELECT * FROM sys.schemas WHERE name = 'MyDbo'))
BEGIN
EXEC ('CREATE SCHEMA [MyDbo] AUTHORIZATION [dbo]')
END
ALTER SCHEMA MyDbo
TRANSFER dbo.your_old_table
GO