Configuring IIS security and permissions?

I'll start by saying that I'm still in college and don't have too much experience so might need a bit of a dummies guide.

I'm building a multi purpose home server running Windows Server 2012 R2. This includes an IIS server that I have running. I'm trying to set up OwnCloud but am struggling to give the webserver write permissions to files and folders that I pasted into wwwroot for OwnCloud.

Here is what im doing:
Windows Explorer - navigate to folder that needs permissions - right click properties - security - edit - ticks the boxes for write and modify for the IUSR username - apply/okay.

However when I still try to set up OwnCloud I get the message telling me I need to change my permissions.

I also tried installing a Minecraft server plug in which requires the use of the web server and that also gave me a 500 error when I navigate to it.

Any ideas would be great. Maybe I'm just doing it wrong.

Thanks