hey i bought 256x256 head text at market and i got a head texture
can i sell it? i mean sell the head text thats placed in that head

If you have not bought the head texture separately, then no, you can not sell it.

Also, you can't use it. If the owner sees you wearing it, he can report you and measures will be taken against you.
And you can sell that head texture if it is inside the 256x256 head texture item, not separately.