I want to change all of my line thicknesses in of my symbology to a 2 within the same feature class. I have about 30 lines. Right now, I have to change it separately with each line. Is there a way to select them all to change them?
If your lines have a different symbology using unique values etc it is still possible to change all the line properties in one go.
In the Layer Properties > Symbology tab you can click the symbol button (See below) and select Properties for All Symbols... You can then change the thickness for all the lines whilst maintaining the other properties such as colour.