I have a 2003 C70..might be the same. facing the engine the is a large hose going from the front over the engine to the rear. disconnect the hose at the top and move it to your left. at the bottom of the the engine/trans is a little yellow plastic dip stick. There is a metal clip that you need to move to release the stick. I stick a large screwdrive to move the clip because it's hard to move the clip and remove the stick.
Be careful because it is easy to break the stick. If you do replace your fluid use ONLY Volvo fluid ( some will disagree) I put Toyata T5 in my C70 and had slipping, poor shifts. Look in your Volvo book and do a
google seach for the best price, expect to pay between $60-80 for a complete flush and fill. Also.. make a fluid level stick out of a plastic strap , making the levels from the dip stick so you do not have to keep trying to use the real dip stick. I broke mine in the tube but was able to get it out.