You can alternate paracetamol and ibuprofen but leave at least 4 hours between doses of the same drug. You can take ibuprofen then 2 hours later paracetamol, then 2 hours later ibuprofen, or even take 400mg ibuprofen and 1000mg paracetamol together if you're in a lot of pain, but be sure to leave at least 4 hours before the next dose.
Both drugs affect your stomach and liver which is why it's imperative to observe the dosage limits. Talk to the pharmacist if you need stronger pain relief- you can buy other pain relief options over the counter.