If we have a digital signature or certificate we must know that has an expiration date. Normally it lasts two years so we must be pending and proceed to renew it a few days before the deadline. Keep in mind that the same day of the expiration date it stops being active and if this happens to us we will have to request it again, but physically.
Telematic renewal
The process depends on the certifying authority that we have used to obtain it and the type of certificate. However, today most of them are renewed in a similar way and telematically. We will have to check this on the agency’s website, since it is a procedure outside the Tax Agency.
Before starting the process we must know that we have to have the old certificate and that the renewal can be carried out during the 60 days prior to its expiration.
Once inside the web we will have to look for the section of certificate renewal. Then different options will appear since there are several that exist, so we will have to choose the one that is appropriate.

Then we will be indicated the conditions of use of the digital signature in force so far and it will be necessary for us to accept to continue. If the certificate is by card the system will surely generate new keys, public and private, so it may take a while.
Application document
In the event that a dry electronic signature renewal is requested, an option will appear for this, and then a document will be generated that will be the request. In it will appear our data, the public key and a legend indicating that the conditions of use are known. Must click on accept or send.
After verifying the request we will receive by email a code, which is the one that will allow us download the renewed certificate. Once we have it, it is recommended make a backup.
This procedure is the one that broadly uses the National Currency and Stamp Factory (FNMT), but it is very similar in most bodies that issue digital signatures.