How often should I replace my thermal paste on my CPU?(Its been 5+yrs)

If the temps are all in the range u like them to be, leave it be.

Are u going to keep the PC after 5 years?

I am beginning to buy new parts for my computer, like the rosewill challenger case for better flow, because it is much much larger than my micro atx case, it supports 5 fans, and has a lot more holes for vent. Also a new HDD kuz mines running low on space, and eventually a new motherboard and cpu.

I'm not sure what temps I should have though. What are recommended?

Whats the CPU?

"68 Celsius just browsing the web right now"

That's a lot.

What country are u in?

Whats the room temp?

If you need help you can read the guide in my signature, I'm pretty sure I addressed the amount of time before you need to reapply TIM.

5 years old, is old nowadays.

If u spend today $300, u can make yourself 3-4 times faster PC.

That is if u are up for upgrading : )

I am buying a new case, the coolermaster storm scout to be exact, aswell as a new hardrive. eventually ill buy this:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

And this motherboard to fit the CPU:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

I have the intel core duo e4600 at 2.4 GHz (ik, not that good)

I mixed up my gaming temp and my browsing temps up.
My GPU atm is 55 Celsius, and hasn't ran a game in two days.

When I DO game though, i get from 68 - 75 Celsius.