Changing property types

[BF1]

I may have messed up on this one. I originally linked my table to a spreadsheet. I now need to add primary keys to certain field but Access will not allow this due to the linked nature - any suggestions? I would also like to change the data type in one field to mixed numbers and letters - does a data type category exist to allow a combination of letters and numbers ? If so, will I still be faced with the linked table dilemma ?
Thnaks in advance

 

[BF1]

A spreadsheet is NOT a relational table. You cannot set a primary key for it.

A text field allows numbers and letters.

Many thanks for the reply - do you have anysuggestions how I can make records differentiate between what are different jobs at the same store without setting primary keys ? Also, how can I change from number to text type in a field if the table is loinked to a spreadsheet as Access will not allow ?
Many thanks