How to Correlate a checkBox with a NumericUpDown

Good afternoon guys, I would like to know how I can correlate a checkbox with a NumericUpDown. Well for more understanding, I made ​​a program which presents a list of products made ​​with checkBox's and beside of these NumericUpDown's which I put in property "enabled = false". What I want is that when the users mark a checkBox the NumericUpDown change its propriety to "enabled = true". I used the following code: 

if(Frt1.checked == true){
      NFrt1.enable == true;

}

where the checkBox is nominated "FRT1" and NumericUpDown nominated "NFrt1", but it didn't work. So I ask you humbly a little help. 

Ps: I use VS 2012 express for windows desktop (C # language).