Changing the blade belt on a Mastercut riding mower.

Hello all,
I've had a Mastercut riding mower for about 10 years that finally shredded a belt.
It's a 12 HP, 42 inch cut.
It's the belt that runs the blades.
I have a new belt, but it looks like it's harder to do than I anticipated.
The belt has to go around several things and I have no idea how to do this.
I'm on a limited income and would prefer to do this myself. The shops cost more than I can afford right now.
Can anyone give me some instruction on how this is done safely and properly?
Thank you for your help
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