The PSU only draws as much power as the system actually uses. Probably much less than 1000W or 750W.
Downsizing to a 750W PSU won't reduce power consumption. It may even increase power consumption (as measured from the wall receptacle) if it has to work harder (and hotter and louder and less efficiently) to provide power to your system than your existing 1000W PSU. In fact, one of the ways to reduce power consumption is to have a decidedly oversized PSU so it's always quietly running light loads at generally peak efficiency.
Buying a more energy-efficient PSU will reduce power consumption (as measured from the wall receptacle). But the price difference you'll pay now will probably take several years (most of the PSU's useful service life) before it "saves" enough money on your electrical bill to actually pay for itself.
If you purchased your M6F in late-2013 then it (and your PSU) are approaching four years old. Unless the PSU had a long warranty (>3 years), it's probably aged and de-rated a little (become capable of delivering less power with less efficiency) - but I still suspect your old 1000W doesn't consume any more power than a new 750W PSU would.
Your M6F mobo has four power connectors: 24-pin EATXPWR, 8-pin EATX12V_1, 4-pin EATX12V_2, and 4-pin EZ_PLUG (Molex connector).
EATXPWR is main system power (required), EATX12V_1 is CPU power (required), EATX12V_2 is more CPU power (recommended, required if overclocking), EZ_PLUG is more GPU power (optional, recommended if GPU overclocking and/or multi-GPU). If you have enough power cables then plug them all in to ensure maximum system performance and stability. If you only have two 4-pin EATX12 connectors then plug both into EATX12V_1 (or one into EATX12V_2 if the physical keying/shape won't fit into EATX12V_1). Many PSUs have hybrid ATX12V/EPS12V connectors which can function as one 8-pin or two 4-pin motherboard inputs.
Any ATX12V2.x-rated PSU will supply 24-pin EATXPWR and one (maybe two) dedicated 4-pin EATX12V outputs, along with a spare Molex for EZ_PLUG
Any EPS12V2.x-rated PSU will also supply a dedicated 8-pin "EATX12V_1" output
Any (full- or semi-) modular PSU will provide a variety of secondary power outputs which can be reconfigured as neededhttp://support.antec.com/support/solutions/articles/1000140052-what-is-this-connector-for-
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