You need to first inspect each suspension component individually until you find which part is loose. It would help to jack that side up, remove the wheel, and safely inspect the components by jostling them. A well-placed crowbar can help.
Any job can be a DIY job. It depends on what tools you have and how comfortable you are at tackling certain tasks.
Suspension components don't necessarily need to be changed in pairs. Just replace what's worn out.
95 E320 Cabriolet, 131K