The tool you have bought is whats known in the biz as a "Kent" tool. It is primarily used for cutting bonded glass out.

However, it is not the best tool to use if you are planning to save the glass (ie not break it)

Screens crack very easily, body glass is tougher, but when it goes it just explodes.

As mk2rstaff said, the best way to get out the quarter glass is with a knife from the inside. The problem with the quarters on Sierra's, is they have metal clips that hold the trims on, that make getting the glass out very difficult. It's almost impossible to use the kent knife to get the quarters out cos of these trim clips, but I have done it, albeit as said, with great difficulty.

The cheeswire is a much easier option. You don't need two people to do it tho. all you need is two wire handles, square cheese wire (the ribbed gold stuff is not a good idea to use as it will destroy any inside trim, and I've seen it cut into metal!) You need to feed the wire inside, go all the way round the glass on the outside (placing the wire between the glass and the metal, making sure to get it between the metal clips and metal of the car so the wire doesn't get caught on these clips) Go all the way round the glass, overlap where you put the wire through the glue about 2 inches and then insert that end of the wire through the glue aswell. Affix the handles to the wire inside and you basically garrot it the glass out - hold one wire handle tight and pull the other one towards the centre of the glass. It's hard, but it will pull through the glue. Small tip - tape the glass up on the outside to the body of the car. Nothing worse that spending all the time cutting the glass out for it to fall to the floor and smash