I did this on my Vectra and its a right bastard! You'll need a small flat blade screwdriver to undo the 2 clips that you have seen. You will need to mark the positions of the blocks on the thin rods before you move anything as these rods are part of the linkage and if they go back in the wrong place you could have some difficulty selecting gears.
So mark off the entry point of the rod at the entrance of the clip/block. Flat blade screw driver to unclip, undo 4 off mount bolts in the floor and out it comes.
If you've got a Haynes manual it'll all be in there. You will then have to unclip the gearstick from the assembly.