If its the same as a saphire/sierra its abit fiddly

You have to change the whole lot on a saph too,different spline on the manual sunroof mech compared to the electric motor

The whole lot can be removed without removing the glass,you have to mess about sliding the sunroof in and out and removing the screws that are accessable with it open or shut
Hopefully for your sake the screws that hold the glass to the mech will not be rusted up,if I remember correctly there are 6 screws,you get to them by removing a small piece of plastic trim on the sides of sunroof.
Then the mech is held to the roof of the car by a load of self tappers which screw in from the outside

Good luck