Civievent - Billing fields
Welcome to CiviCRM StackExchange Kim!

If you think that the translation should be changed for all users that use Swedish as a language in CiviCRM (e.g. because it is wrong or yours is better) you should update the strings in transifex. 

This would imply that you create a free account there and ask to become part of the Swedish translation team. Once you changed the translation in transifex you will need to update your translation locally. You can find information on transifex in the CiviCRM Wiki.

If you only want to change the translation for yourself, you should use the function for word replacement in CiviCRM, which you can find at yourdomain.org/admin/options/wordreplacements?reset=1

On the left side you will need to enter the original (English!) string, on the right side, the one you want to use (in Swedish).