My age is 21 & weight is 46kg.
I desepertely want 2 increase my height.
So what should I do.

The only treatment I know of to increase height is when they break your legs (painful) and stretch the bones apart with screws daily (also painful), but I think they only do that for people who are dwarves. There are no medications. Once you're done growing (A little after puberty starts), you're done growing for good.

There are medications called HGH (human growth hormone), but those are given to very young children before they become teens.

You say your weight is 46kg (101 pounds), but you do not mention your height. Are you male or female?

My age is 21 9Male) & weight is 46kg.
My height is 5feet 5 inches.
I desepertely want 2 increase my height.
So what should I do.

Unfortunately you are a product of genetics. At this age there is no certain way to increase your height.

my age is 21 & weight is 46kg.
i desepertely want 2 increase my height.
so wat should i do.
My son had same height problem when he was 10 year old was size of an 8 year old. Everyone thought I had a little genious on my hands until I told them his real age.
He had an option of taking growth hormone injection over a long period that may increase his height and weight but it would require lots of injections. He chose not to do that which may result in shortv stature. He developed just fine and has a nice deep voice. He grew to 5 feet 7 inches and about 160 lbs. His mother (me ) is 5 ft 6 inches and his father 5 ft 10 inches, so go figure.
I am proud to say he just had if first child at 35 ( I am a happy grandmother)
FYI he had a school friend who was also small who took the growth hormone. He did gain weight but not height. He was a school wrestler as his father wanted him to be. I don't know if it was worth all those shots over the years. My son seems to have been quite content w/his height. His wife of 6 years is about 5 ft 4 inches .
Hope this helps a little.

You are the height you are, that can not change.