First of all, most any Autoparts store is going to have the replacement bulb. Check on the back of your owner's manual for the correct one, but it should be a 60 W, HB-3 bulb. I bought one for our '04 V70 at Auto Zone.
There is a round screw on lid at the back of the headlight. Make sure you get the right one unscrewed and off. The passenger side seems very very cramped and difficult to get off. I replaced the driver's side a few months ago. Once the cover is off, just reach down and disconnect the connector to the bulb. Tape it out of the way, as it will swing back into place and get in your way. Now, there is a metal spring clasp you have to unclasp and then reclasp. I'll let you read the rest directly from the manual (either section or page 120 of your manual)
Do not touch the glass on halogen bulbs with your fingers. Grease, oil or any other impurities can be carbonized onto the bulb and cause damage to the reflector.
Be sure to use bulbs of the correct type and voltage.
Removing a defective bulb
To remove a defective low beam bulb:
Switch off all lights and turn the ignition switch to position 0.
Open the hood.
Remove the plastic cover over the bulb (1) by turning it counterclockwise.
Remove the connector (2).
Loosen the retaining spring (3) by first moving it to the right and then moving it down, out of the way.
Pull out the defective bulb. Note the position of the guide lug on the base of the bulb (4).
Installing a new bulb
To install a new low beam bulb (H7):
Insert the new bulb, without touching the glass, with the guide lug upward (1). The bulb will only seat properly in this position.
Move the retaining spring up and push it slightly to the left until it seats properly (2).
Press the connector into place on the bulb (3).
Reinstall the plastic cover and turn it clockwise until it is correctly in place (4). "TOP" must be upward.
Hope this helps.
BTW, if you don't have an owner's manual for your car, it can be found here: http://apps.volvocars.us/ownersdocs/200 ... c70_00.htm