ThatVietGuy :
Why do you have to disassemble the whole computer to measure the space for a GPU?
All you should have to do is take off the side panel of the case, unscrew the screws that secure the GPU and slide it out of it's socket.
https://www.youtube.com/watch?v=KWuT8oz4BKc
I know it's not the best quality video, but you should get the gist of what you'll need to do.
Basically just take the case panel off and measure where your current GPU is, you can remove it if necessary. Or use pcpartpicker, add the GPU you wish to purchase and the case you have to a part list which should then say if the two are compatible.