I have replaced oxygen sensors on my old BMW as well as a Corvette, but not on the Volvo. Generally, it is no more complicated than replacing a spark plug; the Haynes manual for the S70 doesn't indicate that there are any problems with access or that any special tools are required. Make sure that the Bosch has the same number of wires and a matching connector else you may have to solder or crimp your existing connector to the new oxygen sensor if it wasn't specifically designed for the Volvo. Get the OEM part if there is not a big price difference between the Bosch and the Volvo part. The S70 has two connectors going to the oxygen sensor. Use a dab of anti-seize on the treads but do not get any on the tip of the oxygen sensor else you can dramatically shorten its life. The sensor may already have anti-seize on the treads. Don't drop it. Spray conectors with electrical contact cleaner because unclean connections can cause the same diagnostic codes as a bad oxygen sensor. Torque to 33 ftlbs per the Haynes manual.