Hi People hope everyone is good and having a good day, i am trying cut out a quater of a circle and i have tried using the knife tool but found this rather dificult and have tried the default editing tool and tried inverting the excess inwards but this did not work as well, as you can probably tell i ahve only just started learning how to do 3D modelling on blender. Basicly i just want to get rid of the excess quater i do not need. please see the PNG i have attached.
Any help would be apreciated.
Thank you :) 
P.S. i have done a landing foot and cut corners out thanks to bruno's instructions :) however i do it manualy for each corners and some corners as you can see from the picture are not equaly continuitive :)is there a way that i can duplicate the first cut like for like so all corners are the same :)[![enter image description here](https://i.stack.imgur.com/lyU6K.png)](https://i.stack.imgur.com/lyU6K.png)

Simon[![Screen shot of blender project i need to cut](https://i.stack.imgur.com/3MTqx.png)](https://i.stack.imgur.com/3MTqx.png)