You can check the wear indicators on the tires. These are small raised bars between the treads. If the treads are level with these bars, it is time to replace the tires. Alternatively, you can use a tire tread depth gauge to measure the depth of the tires' treads. If the tread depth is less than 2/32 of an inch, it is time to replace the tires. Additionally, if you observe any cracks, bulges, or other signs of damage on your tires, they should be replaced immediately.