Replacing the slats on a wooden outdoor bench is generally not a difficult project for someone with basic DIY skills. The perceived difficulty often depends on the bench's construction. For a simple bench with slats screwed or bolted directly into the frame, it's quite straightforward. You'll need to remove the old, damaged slats, measure and cut new ones (cedar, redwood, or pressure-treated pine are good choices), sand them, and attach them with corrosion-resistant screws. Pre-drilling holes is crucial to prevent the wood from splitting.
The challenge increases if the bench has complex joinery, like mortise and tenon joints, or if the entire frame is rotted. In such cases, you might need more advanced tools and carpentry knowledge. However, for most common benches, the process is manageable. The key steps are: assessing the damage, selecting the right replacement wood, ensuring precise measurements, using the proper tools (saw, drill, sander, wrench), and applying a protective finish. With patience and careful work, you can restore your bench's strength and appearance, extending its life for many more seasons. It's a satisfying project that saves money compared to buying a new bench.