Help please

[Tamnewbie]

Hi Everyone........as my name suggests I'm relatively new to bonsai (about 6 years) and VERY new to this site. This question is about my (now 2) Liquid Amber's. I thought I'd lost my original small tree, so a few months ago, a very generous member of our local club gave me a well established tree. Now they are both in full BIG leaves. Do I defoliate them both now to try for smaller leaves or leave them alone? My main concern is the ever changing weather, from hot last week to wet and freezing today
Tamnewbie