heater will not blow any air

winter is almost here and i started to try and use my heat the other day on blast and i noticed hardly any air coming out. sometimes when driving fast i get a little better air flow, but as soon as i slow down the air almost dies. my guess is the heater blower is almost gone. where is this located and is it difficult to replace?

under the dash passenger side...should do the blower motor resistor too.