I have a trane xr 13 and the capacitor has went up and I need to know what size I need and where to buy the part from

It may say on the motor, may be like a neighbors.
It would say like 10 uF, 370 volts(10 microfafads@370 volt rating).
Ebay

Like this:
uf 370 volts | eBay (http://www.ebay.com/sch/i.html?_trksid=p5197.m570.l1313&_nkw=uf+370+volts&_sacat=0)
Will see what I can find on the XR 13