Open the Dimensions Property and change to your like.
Move the cursor to the Dimensiontool, leftclick and it's Property open, og down to the Units/Tolerance and change it there, see attached.
Note that you can have max 9 "0"'s but only the number in Presision will be numbers, the rest will only show "0"'s
Like it show in Attached will give you 2 decimals becouse of 0,01 = 2 and presisions = 2
There you also can turn on/ of Append Units ( mm in this case)
After that you can go up to the Format and set the text style/ size you want
V18, V19, V20, V21, 2015 Pro. Platinum
Deluxe V20, V21, 2015
Windows 10 Home Premium 64 bit, 32 GB
NVIDIA Geforce GTX 780m, 1 GB