clean the dust from it. also if you have Q-fan or some similar automatic fan control turned on, it reduces the speed the fan spins at idle increasing temps slightly. Also the ambient temp has to be the same to get a reference temp.
- As mentioned, might be worth buying some new thermal paste and doing a fresh application and reseating the heatsink.
- Not sure where you live, but there are some places in the states with 90d temps right now and you could have a really high ambient temp. (Although probably not enough to make that large of a difference)
- Clean out your case regularly for dust. Wash your removable dust filters (if you have them) and use a can of compressed air to clean out your case. Can actually help more than you would think.
- Did you recently make any changes to your computer such as overclocking or anything? That could easily increase your comp temps, but I'm assuming you didn't.