how to make background white

I would edit the image in Photoshop. Converting the image to Grayscale is one solution. If the image is going to be printed and the dark/black colors of the music notation need to be rich black rather than dark gray I would use different approaches.

If the image doesn't contain more colors than a yellow background and black for the music score notation you could try using tools in the Image>Adjustments>Levels dialog box to turn the yellow color to white. In the dialog box there are eyedropper tools to set black point, gray point and white point. If you click the white point eyedropper onto the yellow background color it will turn white.

The Levels dialog box can also be used to adjust contrast. The slider controls at the left, middle and right ends of the histogram graphic control this. Sometimes I'll inflate an image from 8-bits per channel to 16-bits per channel (using the Image>Mode>16 bits/channel command) before making edits in the Levels dialog box to prevent shredding the histogram too badly. I can drop the image back to 8-bits per channel once the editing is finished.

The Levels command can also be applied as a non-destructive Adjustment Layer via Photoshop's Layers panel. At the bottom of the Layers panel click the round icon for new fill or adjustment layer and choose Levels from the drop down menu.

Of course, Photoshop would be the preferred application to do these image edits, but you can try this in Illustrator.

Conver the embedded image to Grayscale: Edit > Edit Colors > Convert to Grayscale

Followed by:

Edit > Edit Colors > Adjust Color Balance. Turn on the Preview and decrease the Black slider percentage.