TL DR: Check your maintenance schedule, but most likely it doesn't need changed at all. Changing it will not hurt anything, though.
You can check the maintenance schedule for your vehicle, but most cars with a manual transmissions do not require a fluid change. Unlike an automatic transmission, there are very few wear parts within a manual transmission which can cause debris buildup in the fluid, so it doesn't really go bad. Also unlike an automatic, the transmission doesn't build up a lot of heat, which can cause the fluid to go bad over time. Inside an automatic transmission, there are a lot of friction disks which ride against steel plates causing both things to happen. There's also the torque converter which when not in lock up mode will create heat due to the fluid shearing happening when it's doing what it does.
With automatic transmission which have never had the fluid changed, it is often a worry that by changing it with a lot of miles, you might actually be doing more harm than good. Changing the fluid can remove deposits which are actually helping the automatic to continue working. At least that's the theory. Manual transmissions don't suffer from this because the deposits really don't occur.
While in most cases changing fluid isn't required, if you feel you want to change the fluid, it won't hurt anything ... that is as long as you are using the correct fluid for your transmission and you ensure the correct quantity is added.