Deleting fields on project do not delete them on subtasks?

I have a question, just to see if someone can help me. I have been trying different kind of fields in a project and I have found two things that I want to comment here:
1.- Is there any option to make changes inside the field kind (changing it from number to date or currency) when a field has been created? The only way to change it is creating a new one?
2.- If a field is deleted in a project, I am still able to see it in subtasks, is there any way to deleted here too?
Thanks in advance!!

Hello @Sergi_Moreno, that is currently not possible. Here is an existing feedback request for you to upvote: Change field type once in use

Was data entered in this custom field before? Or the custom field did NOT have any data entered across the project?
Did you delete the custom field completely from the org or you only removed it from the project?
If you only remove it from the project but data was added before removing it then it normally shows data like this:

And in subtasks custom fields show like this usually: inherited fields