Basically you have to identify the rows that contain the invalid value and update them with a valid value.

Have a look at:

Troubleshooting DBCC error 2570 in SQL Server 2005 and later versions

http://support.microsoft.com/kb/923247

Look for:

Finding Rows with Invalid Values Using T-SQL Queries

Decimal and Numeric data type:

--

SELECT col1 FROM table2

WHERE col2 > 9999999999.99999

OR col1 < -9999999999.99999

--

Keep in mind that you will need to adjust the values based on the precision and scale with which you have defined the decimal or numeric column. In the above example, the column was defined as col2 decimal(15,5).