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@SuPo. It would be useful if you could upload a smaller photo of the whole plant to get a good general view. Generally, this is an easy plant to care for. It needs plenty of light but not direct sunlight. I think it has been left to dry out before you bought it, and that is probably what has caused the problem.
I would remove all the damaged leaves, and maybe cut the plant back a bit, only water it at intervals - they don't like over watering at all. If you do cut it back you can make cuttings out of the bits you remove as they root quite easily, then you'll have some extra babies too.