The base answer is No you cant use core i5 4570t

A Dell Optiplex 9020 tower could use that processor but not a 760.

You did not say which size you have.  There are no Core I3 I5 I7 upgrades EVER for an LGA 755 motherboard.

https://www.dell.com/downloads/ap/products/optix/optix_760_tech_guide.pdf

The Optiplex 760MT uses two motherboards -
T674K Non-Quad core CPU motherboard
U562N Quad core CPU motherboard

If you use a TOWER with Quad core CPU the optional 305W power supply is also needed.

38G73 E7400, 2.8GHz, 3MB, WFD, R0, (With VT)
F31F5 E7500, 2.93GHz, 3MB, WFD, R0, (With VT)
06YMG Wolfdale Dual Core E7600, 3.06GHz, 3MB, 65W, R0, (With VT)
H399J Wolfdale Dual Core E8400, 3.0GHz, 6MB, 65W, E0, 1333FSB
D923J Wolfdale Dual Core E8500, 3.16GHz, 6MB, 65W, E0, 1333FSB
N654J Wolfdale Processor E8600, 3.33GHz

MT DT SFF USFF