Responsibility for the decoration of leased premises all depends on the agreement between the landlord and the tenant. Hopefully there is a written lease which has been prepared with these things in mind.
There are three main ways a lease will deal with decoration – it will either be the responsibility of the tenant, of the landlord or a mixture of the two. The landlord will often be responsible for the exterior of the premises where the lease is of part of a building. In that case the landlord will decorate the whole of the exterior and send a bill, perhaps as part of a service charge, to each of the tenants in the building. You will usually find that the interior of the premises is the responsibility of the tenant. Leases will often define the terms "exterior" and "interior". For example, "interior" may include the exteriors of the doors and windows.
If your lease is short term, and of quite small premises, you may find the landlord has included the cost of exterior decoration in the rent, but will rarely agree to decorate the interior.
Where your lease is of the whole building it is more likely that you will be responsible for maintaining the exterior and interior of the premises.
A properly drafted lease will say how often the premises need to be decorated, and to what standard. The lease may say that the premises should be kept "in good repair and condition" or that the premises need to be decorated every three years for example. The obligations vary widely, so it is worth looking at the lease carefully. If you are about to lease premises then consider these aspects carefully before signing up.
If there is no written lease you will have to look back to the time you leased the premises for evidence of what was intended.