I followed the youtube block method along with McNeel article.
Created a 1mm sphere, ran block command, chose centre, and named it. Sphere
deleted the block as Mcneel said and created instances .
Selected sphere and 3Dscaled it factor 2 from centre and typed block, selected centre again, selected my block name sphere and it does as it did on youtube vid asking do you wish to replace, I go yes, …
and it says this name already exists, choose another ! and so my 1mm spheres wont become 2mm spheres.