Here's the article I referenced but mine were way harder to remove than this page made it look:
- Reciprocating saw
- Wonder Bar (thinner than a crow bar so you can get it into tight places)
- Crow bar (much beefier than a wonder bar)
- Concrete Chisel
Highly Recommended Tools:
- Oscillating tool (This is probably the greatest tool I own. You can probably do the job without it but, if you don't already own one, just buy it. You'll use it for every project hereafter.)
With a reciprocating saw make cuts in all sides of the window frame. Be careful you're not cutting into the wood surrounding the frame. Sometimes the steel wraps around your wood framing so stop short if this is the case.
Extend your cuts using an oscillating tool with a metal cutting blade. The longer the blade, the better.
Loosen up the bond between the metal and concrete as much as possible by running the tool around the perimeter of the frame. If you have a masonry bit this will work best.
Use the concrete chisel and mallet to beat at the frame right where it meets the concrete. This will help loosen it up and may help create a crevice where you can fit the crowbar.
Start trying to pry away at the frame anywhere you can get a crow bar into. The more you pry down on the frame, the more access you should have to cut the frame all the way through.
Keep on prying from every which way...
Finally! Well that was stupid...
And now, because I'm anal (and because it will make shimming WAY cleaner and not a Dick job), patch that chunky mess of concrete with more concrete.
Yay, now install your window per the manufacturer's instructions!
These are just cheap Jeldwen's from Home Depot but are WAY nicer than those crappy aluminum ones ghetto mounted to 70 year old frames.
And don't forget to spray foam (low expansion) and caulk. We don't need any bug passageways like Dick installs. (I taped the front of the window because I spray foamed from the other side and didn't want it squeezing all out on the painted portion of the window.)