Both brake pads and discs last between 25000 and 50000 miles in general dependent on how the vehicle is driven and it is best to replace them at the same time.
Replacing brake pads and discs will take a few hours and can be performed by anyone with basic mechanical knowledge, DIY skills and a few tools detailed below.
If uncertain a visual inspection of brake disc and pads condition can be key. Most rims allow visibility for these parts and the brake pad thickness must be at least 6.4 mm. Brake pads and discs must be replaced in pairs (front and rear) to provide even grip when braking.
As this is DIY tutorial let's presume You don't have access to a car lift.
The need for an impact wrench may be necessary if some bolts are stucks, although it's always useful to have and will make the whole process faster and easier.