how to change target platform from anycpu to x86

I think you have posted screen shot of solution properties. i.e. you did right click on solution -> properties and show this.

 

the setting you want to do is under project properties i.e. select any project (individual project, not the top level solution) -> right click -> properties -> Build, then under platform targer, you will see x86 and x64. you will have to do this for all projects in your solution.