TWI Arduino Uno to Si 570 synthesizer, Internal Pull ups disable.

Using Arduino Programming Questions
1

I am using the I2C protocol to load a Si 570 synthesizer which runs at 3.3V.
The wire library attaches pull ups to +5 internal to the chip.
I need to pull the SCL and SDA lines to 3.3V externally.
I found the following suggestion;

This means everyone will have to re-do the change that disables the
internal pullup on their computer. The file that needs to be modified is
actually twi.c, not wire.h.

On a Windows machine, go to: c:\Program
Files\Arduino\libraries\Wire\utility\twi.c

And comment line 76 and 77:
// activate internal pullups for twi.
//digitalWrite(SDA, 1);
//digitalWrite(SCL, 1);

But, twi.c is not at this location. I know that it exists because I included wire.h to my libraries.

2

But, twi.c is not at this location

It would be if you had installed the IDE in C:\Program Files\Arduino. I don't.