How to Change Decimal in Excel

If you want to change a decimal number, the digits behind the comma, either reduce or add to it, you need to do is: 

1. Select the cells you want to change the numbers 
2. On the Home tab, in the Number group, click the Decrease Decimal (decimal Reduce, reduce the numbers behind the comma) or next to Increase Decimal (Add a decimal, add the numbers after the decimal point).

The two function buttons just change the number of digits after the decimal point, not decrease or increase the value of the number itself.
For example in the figure below, the first line of 12.12. at Decrease Decimal to 12.1 or in-Increase Decimal be 12.120, all the value of that number remains the same, namely 12.120.

Now if you want to set up the Excel so that the numbers are typed / input on a cell becomes automatic back into decimal numbers, then you can use the option Fixed Decimal. In Microsoft Excel 2007, follow the steps as follows: 

1. Click the Office Button 
2. Click Excel Options menu located on the bottom right. 
3. Click the Advanced tab in the left column on the pop-up window. 
4. In the Editing Options in the right-hand column, check the option Automatically insert a decimal point. 
5. On Places, fill with digits after the decimal point you want to take from the numbers inputted. If the contents of your 2, then Excel will take 2 numbers into the decimal rear. For example you enter 12345, the automatic will be 123.45

 That is called Fixed Decimal.

Well, what if the case is you already enter the lot number 12345 with the format and then you want the figures had to be 123.45?

For cases like this, I have not been able to find a way. However, a solution that you can do easily is to divide it.
Make a new formula in the column next or line below. If you want to change in two decimal places, then divide each cell with 100. If you want to turn it into one number after the decimal point, then divide each cell with 10.

Numbers denominator or Divider:
10, then to 1 decimal places
100, then to 2 decimal places
1000, then to 3 decimal places
10000, then to 4 decimal places Etc. 

You do not need to do it one by one. Simply by way of Auto Fill Options, namely drag and drop down when the form of the column, or to the side when a line.
Drag it to the cell you want to fill (see picture above). Will automatically change all. Maybe that's the solution. Please ask if there is still trouble.