Can you kindly explain in simple language how to do this so that all projects have the same percentage? Using latest edition of Boinc

You need to go to each project's preferences separately, and set the resource share number. It doesn't have to be a percentage, what matters is the ratio between the numbers (i.e. they can all be 100, which is the default setting).

If you are asking how to change all projects to the same value with one operation, I don't think that can be done.