Advice on fitting new UPVC windows please

[1066]

I aim to replace two small critall windows for upvc units. They are about 130cm x 60cms with just a single opening fanlight at the top. I already have the new units and they will be a direct replacement.
I plan to do the job myself (I know about FENSA) but I could do with some advice about the bag of packing pieces supplied with the windows. The units are REHAU and I have about 20 green 5mm packing pieces and about 10 blue 2mm.

Are the packing bits used just to shim up the glass to centralise it in the frame or am I missing something. Any help would be appreciated.

 

[swelec]

http://www.u-fit.co.uk/windows/fitting/FittingGuide.asp

read this first - come back if this does not help

 

[Richard C]

I plan to do the job myself (I know about FENSA) but I could do with some advice about the bag of packing pieces supplied with the windows.

If the windows will not be covered by FENSA, just a reminder that replacement windows should be notified & inspected by BC to get that all important compliance certificate.