How do you replace track on terex mini excavator?

Lift the faulty track of the ground by raising the digger with the dipper arm.

if you look at the middle of the carriage that holds the track (between the drive sprocket & idle wheel) you should see a small steel plate. This is normally held in place with 2 bolts, remove it & you should then see a "Grease Nipple". If you screw this out you will then be able to push (may need knocked back with sledge hammer) the idle wheel back along the carriage, giving you enough slack to put the track back on. Screw the nipple back in and pump with grease till the track had reached the required tension.