Select the object and change the properties. Unfortunately you may have to carefully select each object (presuming you have may objects) to apply the changes. This process was much easier in windows version using Qselect, where u can select objects based on a criteria.
Current object properties are the properties shown in property inspector when no object is selected. Basically it provides the set properties for new objects. Changing any of these properties will only affect the new objects. All objects created prior to the change will retain their existing properties.
Object properties are not shared parameters. Every object has its own copy of parameters. The only way to make them share a value is to assign Bylayer, Byblock value to them ( It can also be done using parametric equations). The former will share the properties of the layer and later will share the properties of the block.
I hope I am making myself clear. Let me know if you have any difficulty in understanding.
KC
