A Freeview box is ideally used for UK Digital TV via a TV Aerial. If used in Spain, it receives the Spanish digital channels.
To retune a Freeview box you simply go into the menu system and perform a new scan, it will scan all available frequencies and it keeps the channels in its channel list.
However, in Spain in the last few months some Spanish digital terrestrial channels have changed their frequencies, as part of TDT Phase 2. Reception of these channels will depend if your community aerial has been "upgraded" to use the new frequencies. If it has, then a scan on your Freeview box will pick up the new channel on the new frequencies.
see tdt1.com and select your area and you can see which channels are on which frequencies.
Not too sure what you mean by "We have a old digi box that for some reason doesnt store the new frequency", as some a Freeview box has scanned it should keep the channels in its channel list, and use those frequencies for the channels.
But by using the term "digibox" you are now refering to a Sky box, which it totally different to a Freeview box, and a totally different system! Maybe by saying "it does not store the new frequency" you mean it does not keep the default transponder frequency you manulally input. Well thats normal and it may not hold that manually input frequency. Infact once you have channels, that manually input frequency is ignored! You only change the default frequency to help the sky box boot up.
If you want a bit more help then make and model of the box you are having problems with would be useful, and if you are on "direct from satellites" or a private "cable" or "rebroadcast" network.