I know, shocking

.
If theyre old and tired (which they probably are) its best to replace them in pairs. Ie both front springs.
Its fairly straight forward. You will need a set of spring compressors and know how to use them PROPERLY as an incorrectly compressed coil spring can be VERY dangerous!
A very quick guide....
Jack up and support the front of the car and remove wheel.
Remove the 2 bolts securing the strut to the hub (might want to soak them with penetrating fluid the night before)
Disconnect the brake pipe from its bracket on the strut.
Remove the bolt from the top of the strut (top of suspension turret in engine bay)((you may need to hold the center of the strut with an allen key whilst you use a ring spanner if you dont have access to a windy gun))
Remove shock and spring assembly from the car.
Use spring compressors (at LEAST 2 preferably of the type that lock to the spring so that they cant fly off) to compress the spring and take the tension off of the top mount.
Undo the top retaining nut and top mount, slide compressed spring off of shock.
Carefully uncompress old spring.
Fitting new spring is reverse of removal.
I do
STRESS though, that working with compressed coil springs CAN be very dangerous, so be very careful and make sure you are aware of what your doing! If you are unsure about ANY part of it then ask here and one of us will help you.
Alan