It's definitely worth gently extracting any dust and fluff from the back of the Mac and the fan. As far as I know you can't swap out the processor PC-style.
You might have a look at TG Pro from TunaBelly software which will offer you some useful monitoring and where you can boost the fans in case of overheating. But, their notes would say that 85deg. while high, is not excessive.
Specifically, from their monitoring advice:
Green - The temperature is between 0 to 89C (32 to 192F) and is generally nothing to worry about
Orange - The temperature is between 90 to 99C (194 to 210F) and is getting closer to the thermal limit of the hardware.
Red - The temperature is at or above 100C (212F) and it very close to the thermal limit. It's a good rule to not let components run this hot for an extended period of time. It's usually a CPU sensor that will display a temperature this high. Most of the Intel CPUs have a maximum of 95C (203F) to 105C (221F) at which point they will slow down to avoid damage.
Hope that helps