Can not change field data type

[rm.harper]

So in my database i have a field for Tonnage (quantity)

I need for example to input 38.60 or 37.89 so my values must have 2 decimal places, ive searched and found changing my field type to double or decimal should solve the 'numbers rounding up/down' but access will not let me change the data type? Could anyone help me please

 

[pr2-eugin]

Why does it not allow you to change the Data Type? Also 38.60 is = 38.6