In otherwords, how can l do it and what tools will l need? :) cheers

What ball joint?

You will need:

13,16,17,18,19mm spanners & sockets (preferably 1/2'' drive).
A big bar/lever
a short extension bar for ur 1/2'' sockets
a BIG hammer or hydraulic press (capable of 10 tonne)
wire brush
WD40 or similar.
Jack & axle stand.

l will give instructions for O/S wheel for ease of reference, but both sides r done exactly the same.

Jack up O/S/F wheel & support the car on axle stands.
Remove the wheel.
There is a bolt that connects the ball joint to the bottom of the hub. Usually a 17mm bolt head & a 16 or 17mm nut on the other side. Remove this bolt & nut.
Insert ur big bar from the front of the car, over the lower arm & under the floor of the footwell & lever the ball joint out of the hub. (it may be tight, get someone to stand on the end of the bar & then hit the bar with a big hammer)
Now moving to the inner end of the lower arm.
There r 2 bushes holding the arm to the subframe.
Remove the bolt holding the front bush in place, usually an 18mm head. Sometimes the nut on the other end is caged sometimes it is not & sometimes it is meant to be but has rusted off.
Now remove the bolts holding the rear d-bush to the subframe. These go up through the subframe & bush from underneath. One is 13mm & the other is 16,17,18 or 19mm (i can not quite remember which!)
Remove the complete lower arm, which may take a bit of wiggling to get it out.

Now it is time to replace the actual ball joint.
If u have access to a press then use it to press the old joint out & the new one in, otherwise roll up ur sleeves & use a big hammer.
These joints usually press out with 5 tonnes of force, so u might not get it out using a hammer, it all depends how strong u are.

Press the new joint in using a socket on the edge of the joint so that the force does not damage the joint.

Now refit the arm in the reverse order that u took it out in.

When refitting the ball joint into the hub ALWAYS fit a new nut & bolt as they r high tensile bolts.

This will probably take u quite a while to do depending what state the nuts & bolts r in.
l would recommend taking it to a garage to do as they should have the job done in less than 1 1/2 hours.


EDIT
Trevor is additions r quite correct.
l have seen someone hammer the ball joint out of the arm, & the arm does not break providing it is properly supported in a vice. However, the man that did that is an OX of a guy! l doubt that l would be strong enough to do it. The press would certainly be a safer more professional option.

l really appreciate reading VON is answer. Finally some real mechanics here. l would like to add:
1. Before using a long lever bar to pry the lower arm downwards, use a small jack to keep the brake disc & hub upwards. The shock/strut will force it down too, as u pry downwards. Careful, the brake disc can spin off the jack.
2. Use a pry bar or steel pipe that is 6 feet long. You r not strong enough to push on 3 feet.
3. l have never hammered out a ball joint. l am afraid that the cast iron arm will break or crack from direct blows. A new complete arm with ball joint costs around 80 euro, 60 pounds? u decide. ball joint alone price.idk.
good luck.
4. DO NOT ALLOW the hub (left side!!)to be pulled in an outward direction, then it comes out of the gearbox & u lose gear oil on the ground.
5. Tools? u need a torque wrench to tighten these lower arm bolts to specs. NOTICE which direction the bolts go, head facing front? or back? this is important according to repair manuals.