Doors and Windows - window removal

My house was built in the 60's and is a brick one story on a slab, we have the old style aluminum "slider" windows the ones where only one side actually slides and the other is stationary. I am looking to replace them myself but first need to find out how to remove the old ones.they slide on what appears to be a plastic type track that has really spoiled over the years and are not that efficient.I have removed the track looking for maybe a hidden screw or something but cannot find where the mounting screws are located.Please help

From your description, it sounds like the frames are mortared in. The nail fin is embedded in mortar between two bricks. Would be much simpler and quicker to leave the frames in place and retrofit windows to them. Call a couple of glass shops and a couple of retrofit contractors to get price quotes. The windows will be custom made for each opening. That should take about 2 to 3 weeks. Installation, if you let one of the pros do it, will take a day (2 tops) for the entire house. When you select the brand and style of window to install, SHOP THE WARRANTIES!! A cheap price means a cheap window about 100% of the time. Also read the festation ratings for each brand. This is to windows what the MPG stickers are to cars. You don't need to understand exactly how they are arrived at, just that the lower the number, the more efficient the window is, and the more it will lower your utility bills. Also check with your local utility. Many are offering rebates and other incentives for upgrading your windows. See if your's does, and what is required to qualify.