If you weigh over 90kgs you will never be good in the hills.
If you are above 15% body fat you will never be good in the hills.
The first one you might never be able to change short of cutting an arm off.
The second one costs nothing to change and will by far have he biggest effect.
If you are under 15% b/f then you just need to get out and ride some hills, try and pick a gear you can stay in the saddle all the way then over time you can use 1 gear more and go up quicker.
Focus on steep road hills not off road where technique, tyres and power are all important factors in getting up a climb fast.