hi
There are two main types.
One with a wedge gasket internal, you'll need to remove this first thus loosening the external beads for removal.
Two with double sided tape internal, this type you would need to remove external beads and cut tape with a thin sharp blade or scraper , new tape should be fitted prior to unit.
We normally use a ladder for external beaded but take care carrying a double glazed unit up, our guys have been doing it for 30 years.
Depending on size you could pass the unit through the opening to the person on the ladder. Regards Phil Windowseal.
Externally glazed windows are generally not regarded as secure as internally glazed.

You will know if they are external beaded by looking on tje inside of the window.
If the frame is complete and no thin gap,then the windows will be external beaded.
Glass can still be fitted,just a bit more awkward

If your existing windows are externally beaded and your replacing just the glass then you have an access problem and would probably require scaffolding for fitters safety
If you are changing the Upvc windows completely then always go for internal beading

The panes would need to be fitted from the outside off either a scaffold or a ladder. Glazing tape would need to be cut from the inside using a scraper or don carlos first before removing the beads. If there is a sash once beads have been removed you may be able to put your hand through on the inside and push the pane towards you. Glazing tape will need to be replace before installing new pane.

Internally glazed windows are recommended for practicality and security.

Earlier upvc windows are externally beaded and the glass is secured on a security tape, it is not something I would recommend, glazing upstairs external windows is very awkward, whereas internal beading makes the job so much easier and security wise,upstairs and downstairs cannot be accessed externally giving a more secure window.
Hope this helps

Hi,windows and doors are all now using the internal bead fitting systems and this is due to the ease of fitting and mostly the security aspect.

There will be some form of gasket internally ie a wedge gasket which you remove then take the beads off externally or double sided 4mm which if this is the case you need run a knife round before removing then replace. My advice leave to someone who knows what there doing.