Switching from YMS Tier 5 to Partner Visa

Hi All,
Many thanks in advanced for your help. I am getting really confused by the UK border agency website as it seems to go around in circles with information.

I am currently on the Youth Mobility Visa Tier 5 which expires 1 August 2014. I have been dating my British Citizen partner for approx 14 months, however we do not live together. We have recently become engaged. I work full time and have done so with the same company ever since I arrived in the UK. I just want to know what my options are;

1. Can I switch from YMS Visa to Partner Visa whilst in the UK or must I return back to Australia and re-apply?
2. If I can 'switch' how far in advanced would you recommend applying before my visa expires?
3. Can we still apply even though we do not live together?
4. If we are already married, does this make the process alot easier? (We plan to wed this year, depending on if I have to return home or not)

Thanks!!

As you haven't been living together, you must be married, etc., before you may switch to FLR(M) (preferably before your leave expires).