Is it easy to bleed the breaks on a 240? Do I need a second person to do the job? How is it done?

Also is it easy to replace the front pads?

You may have a valid reason to bleed your brakes. If so, have an assistant to open the bleed valve(s) when pressure is applied to the pedal and close the bleed valve when the pedal operator indicates 1/3 or 1/2 of pedal travel has been applied. Repeat this 3-4 or more times as necessary to remove any indication of air spitting out of the bleeder. On the other hand, if you do not currently feel a 'spongy-ness' when you put the pedal down, there may not be a need to bleed the system. In other words, if the pedal is solid when applied you do have air in the lines. Because air compresses you would feel that spongy kind of pedal, hydraulic fluid does not compress and gives you a very solid bottom to the stroke. If solid pedal, then you only need to replace the pads. Don't open the bleed valves but only push the piston back into the caliper with a C clamp while having the top to the master cylinder off. Do so slowly so that you don't squirt brake fluid out of the cylinder. When finished, make sure to build pressure back up in the brake system by exercising the pedal BEFORE putting the car in gear.

I'm doing this because I was told the brake lines need to be flushed. The fluid does look a bit dirty. Is this the correct way to do it? There is no spongyness when the brakes are applied. I've just finished the pad replacement.

I don't think I would based on what you just said. Since you have no current problem with the pedal and presuming you do not see moisture in the master cylinder there isn't any reason to have to change the fluid. Hydraulic (Brake) fluid doesn't go bad. I can't imagine anyone has had the lid to the master cylinder off for any length of time to allow dirt in, so what you see as looking a bit dirty may only be looking into the blackness of the fluid. Bleeding the lines itself, especially since you have no air in the lines, is a fairly easy job for two people, even if 1 is a complete novice and only operates the brake pedal. The person on the bleed screw must be very explicit and tell the pedal man never let up on the pedal until "I" tell you it's ok, because you could suck air into the lines from the bleed screw. So open the screw when the person presses the pedal, let fluid squirt out by opening the screw and then close the screw and tell the pedal(er) to let up and pump the pedal a few times and start over with the bleed screw. I would first consider where the car has lived before trying to break the bleed screws loose. If it's been in the snow, ice, and salt you run a very high risk of breaking the bleed screw(s) off and then you'll need to be good at using easy outs, or you'll be at the service station paying them. All in all, I wouldn't do it in your case.

The important thing to do is NOT to pump the brake pedal to the floor if you are not using a bleeding instrument or else to rely merely on gravity bleeding. I have ruined a master cylinder pumping the brake pedal almost to the floor and so has a supposedly competent mechanic.I would not pump the pedal more than one third of the way down.

Get a manual to guide you thru the process. Up till about '90 or so, the 240's all had the redundant braking hydraulics, so the front calipers have 3 bleed ports and the rears have 2. Unless you have invested in a pressure-bleed tool, you will need an assistant.

Overall, replacing the front pads is quite easy. Including jacking the car up, the whole job now takes me under an hour. Again. pore thru a manual to get a sense of what needs to be done.