How to release memory used by child forms in multi form c# app?

Question

Hello all, I really hope that here i can find some help, tnx. I`m building a multi form c# application it has lots of forms opened in a parent form. The problem is that when i open a child form memory jumps from 15MB to 20MB, i close that child form memory stays on 20MB, i open same form again memory jumps to 25MB, etc. same goes for other forms so my question is how can i optimize memory usage of my application (how can i release the memory used by my forms when i close them). I hope some1 will find a bit of his time to help me tnx.