Fitting no4 rear sight

Hi all - as a complete dunce all things gunsmithing wise I thought I'd seek some advice before carrying out what, on the face of it, is a simple operation. I want to replace a number 4 rear sight. The current one is a mk1 with the normal pin/screw back fitting. Is there anything more to it than getting out the pin (any suggestions how appreciated) and just putting the new on on?
Thanks

No, not really. Drift out the small pin on the LH side, upwards is best if you can, and ease out the larger pin to the right. Just don't let the sight plunger & spring go flying off to "Unknown Land".

You'll have to align the cross pin so that the little retaining pin hole is vertical upon reassembly. Usually its in line w/ the screwdriver slot opposite.