As you might imagine this is not easy.
If you have a rubber gasket you can use a sharp but sturdy knife to cut the gasket then you should be able to remove the glass.
If the windscreen is held in with "glue" (very common these days) you might be able to do the job with a steel wire and some wood sticks.
First you will have to find a spot where you can feed the wire thru the glue from the inside and pass it thru to the outside. Then, with a helper outside you would work the wire back and forth and work it around the perimeter till the glass is free.
There are also commercially available tools that do the same sort of thing, some even have a heated blade to cut quicker.
If you have a rubber gasket you can use a sharp but sturdy knife to cut the gasket then you should be able to remove the glass.
If the windscreen is held in with "glue" (very common these days) you might be able to do the job with a steel wire and some wood sticks.
First you will have to find a spot where you can feed the wire thru the glue from the inside and pass it thru to the outside. Then, with a helper outside you would work the wire back and forth and work it around the perimeter till the glass is free.
There are also commercially available tools that do the same sort of thing, some even have a heated blade to cut quicker.