How do I make OpenOffice my default programme?

Hello everyone,

I have recently purchased a Mac OS X Yosemite. I am very happy with this purchase but I want to make OpenOffice my default programme for text documents and spreadsheets as opposed to "Pages" and "Numbers".

I have already tried changing things for some individual documents - I right clicked a spreadsheet document and set it to "Always open with this programme" after using "Open With" to locate OpenOffice but that doesn't work. I double clicked the same programme afterwards and it still opened with "Numbers". I want to set OpenOffice as the default for all my related documents, not just one or two anyway. It'll make things much, much quicker for my workflow.

Any ideas?

Any help in the form of a blow-by-blow idiot guide would be greatly, greatly appreciated.

Thanks,

Cesar