Can I renew my patent?
You must renew a patent as required by the national laws. If you do not pay renewal (maintenance) fees, the patent will be invalidated.
In most of the countries, to renew patent the maintenance fees must be paid every year (European countries, China). But in US, for example, only three payments are needed (after 3, 7, and 11 years).
In some countries, the payment of maintenance fees starts after the patent is granted (China, Taiwan, US). In other countries, you need to pay also during the time the patent is in the examination stage (European patent).
The patent is valid for a maximum of 20 years (with the exception of drug patents, that can have additional 5 years of protection). After this term, the patent cannot be renewed anymore. What can be done, is that the improvements of the earlier patent can be also patented. In fact, most inventions are improvements of existing technology and a lot of inventions have more than one patent protecting them.