WordPress blog hacked

My website https://www.headstudios.com.au was hacked recently. I found out about this yesterday. While browsing my website I noticed clicking on the ‘Blog’ link would direct me to a page with a black background and some offensive writing.

Further, I found that my WordPress password had been changed. I hastily reset the password and got rid of the Blog link from the Menu. At least our web page is still presentable, however it leads me to ask what I should do to:

a) Prevent this sort of hack attack happening in the future
b) Put the fully functional blog back into operation

I understand that more information may be required and I would be happy to provide it.