I've screwed up many a board when I first started (CPU/NAND BGAs)
Mask all the components you don't want to blow off with kapton &/or tin shields
Preheat the bottom of the board with a (can be cheap) pre-heater with the board clamped at the edges (use heavy base clamps or DIY/large metal units)
I like to monitor the board temp with a hand held non-contact laser thermometer (cheap)
Then use your hot air gun.
Don't try to pull anything off..the solder should
all of a sudden look shiny..then "slide" it, if you can..if not..then it's not hot enough. Heat it more/bump higher temp& then pick it off with fine tweezers
Larger BGA's will need a larger heat gun (modified paint stripper - really!)
Experiment by clamping an old motherboard upside down above a concrete floor (garage?)
Wear safety boots (gloves? your call) & heat it up with a heat gun..moving the gun back & forth, alternating heating the underside, and the top - until components drop off..really!
Hence the safety boots..
Bit of a learning experience..but then you'll kind of get the feel for what it takes for the solder to melt ..without charring a board or ripping up traces/pads