This is a great question and one that will definitely come up during the life of the property.
Often the best time to do this is when a tenant vacates the property. It is always much easier to do these things when the property is empty.
The downside is that you will be without rental income during the period of time it takes to get the work done. The upside is that you may well be able to increase the rent as the home will be much more appealing freshly painted and with brand new carpets.