Subject: how do u represent a reverse in velocity in the space time diagram?

Hi there , here is my question 

At t=t'=0 a traveller sets out from earth with velocity u=+0.5c. The traveller 
is identified with the frame reference O'. He travels for 5 years (according 
to his clock), and then suddenly reverses direction, returning to earth with 
the same speed. 
Plot the world of the traveller in a space -time diagram and Show that for O' 
his line of simultaneity when his clock reads t'=5 years just after turning 
around satisfies: 
t=7.22-0.5x


I am not sure how to show a change in speed in the space time diagram. When 
the traveller is moving away from the earth , the ct'-axis and the x'-axis are 
both in the first quadrant. (the world line of a photon bisecting the both 
sets of axes) And the ct'-axis is the traveller's world line , ( I think) . 
Now, what happens when the he reverses his direction , does the ct'-axis and 
the x'-axis both reflect about the ct axis? 

For the second part I used the Lorenz transformation , and I ended up with : 
t=7.44 - 0.5x .

Any help will be highly appreciated.

Re: how do u represent a reverse in velocity in the space time diagram?