Make a character stand from a sitting position

Hello, I have been trying to find a video tutorial of basicly having a character transition from sitting to standing and return to sitting. 

Some context. I want to create a character for my streaming and she would be predominatly be sitting but when i need to rage i want her to stand and do some animations and then sit back down. does anyone know

a) where i can find a tutorial or documentation on how to do this

b) do i need just two different torsos for my body (one for standing and one for sitting)

thanks in advance

Shannon