The full information can be found in English and directly from the Endesa and Iberdrola websites.
Please note* That rental is charged for the new meters and are fitted free.
In communities the housing for the meters is the responsibility of the community.
Do navigate their websites so that you may be informed.
Smart Meter Endesa
Smart Meter Iberdrola
If the electricians that come to your property to exchange the meter, find any sub-standard situation, either with regards to the placing/housing of the meter, or with regards to the electrical installation, they can request owner to adjust the situation, to meet regulations, at his/her cost, before the new meter is installed. Requirement to produce an up to date ´bulletin´ could be one of the requirements, if the installation is older than 20 years, or suspected to be faulty.
Would advise to ask for several quotes for the work to be done.