You can use StringBuilder to Replace or Remove.
Try this:
StringBuilder sb = new StringBuilder;
sb.Append("exec InsertComputerInventory '844272','345661327','XJ51X99W2','Invoices','2013-5-7','2013-5-9','2013-5-9','24','1','4HRKDW1','Notebooks','INSPIRON 3521','2014-5-9','IKDT','DIRECTOR','IKDT DOLDRUM INST 036','IKDT DOLDRUM 036','1980 METRO COURT SW','WYOMING','MI','49519-9618','6164061200 ','IKDT','DIRECTOR','IKDT DOLDRUM INST 036','IKDT DOLDRUM INST 036','1980 METRO CT SW','WYOMING','MI','49519-9618','036'");
sb.Replace("InsertComputerInventory", "");