How to do Mesh settings

My antenna dimensions are 9cm X 8.93cm with ground plane dimensions 120 cm X 120 cm( operate at 150 MHz). To analyze it, My RAM memory is not sufficient. So I want to change the mesh settings so that the no. of triangles would be reduced and RAM would be sufficient. But I know nothing about mesh settings. I request you to please help me to get the information(what options need to be changed).
I used cylinders to create copper wires.

What software are you using?

Can you use symmetries for reducing the model size?
This would lead to better results since if you are reducing the mesh size, the result can get inaccurate.

I am using HFSS 13 version.RAM is 4GB (with 2.93GB usable). yes, I can use symmetries. But I don't know how to use symmetries.. Please help me to use symmetries and reducing the mesh size( eventhough results are inacurate). Explain me step by step.