Problem about DLL unloading

Hello,

I have a C++ dll which uses C#.net code by clr(Consider DLL A).

Now I'm using this dll into other C++ dll(Consider DLL B) by LoadLibrary function. After completing my work, I'm unloading this dll(DLL A) with FreeLibraby API and try to delete that loaded DLL(DLL A).

But I'm not able to delete this DLL(DLL A) as it is not unloaded from my Client DLL(DLL B). 

How can I unload this DLL(DLL A) and delete after using it.

Thanks in Advance.