Slimming is not just about Weightloss

In fact, one can get some (dress) sizes slimmer and even gain weight. How is this?
Muscles (and bones), the Lean Body Mass , are heavier than fat. So a lean, muscular body can be heavier than a fat one.

Am I Overweight?

Grossly you can do some sums to find this out by comparing your weight and your size very simply: Size minus 100 centimeters in kilograms is normal, ideal weight would be
170 cm ==> 70 kg ,  
for women:    15% less  ==>   59,5 kg
for men:      10% less ==>   63 kg

A bit more precise is the determination of the ideal weight  by the Body Mass Index (BMI), which indicates the body weight per square meter.

Below    18,5  kg/m²   is underweight
above    25,0 kg/m²  overweight.

Computation: 
A person of  1,70 m ==> 1,70 m x 1,70 m = 2,89 m²
Weight:  80 kg ==> 80 kg / 2,89 m²  ==> BMI  27,7 kg/m²
Weight:  70 kg ==> 70 kg / 2,89 m²  ==> BMI  24,2 kg/m²
Weight:  59 kg ==> 59 kg / 2,89 m²   ==> BMI  20,4 kg/m²
Weight:  50 kg ==> 50 kg / 2,89 m²  ==> BMI  17,3  kg/m²

Ideal for women:  22 kg/m², for men 24 kg/m²

(Now it's your turn - you will certainly find other numbers....
10 kg  =  22.05 lb ,  100 cm  =  39.37 in )

These figures can tell you grossly, whether you need indee to lose weight, or you have to do other things to get in shape - mostly more moving and at least slight training.