1.)If i made slight changes in the vector then can i sell the images.
Any resemblance to original product may draw an adversity and the original vendor may jump inside with legal actions.
2.)How much % of the vector should i change to sell the image.
for example : consider the vector is 100%. what is the % should i make change in the vector such that i can sell the vector. (change may be like design , color, etc)
You cannot make any changes in the vector on your own which will again draw the ire of the original vendor who is protected by trademark laws on the product he sells.
3) what are the terms should i write on my website.
There is no question of any terms for selling the product when you are not entitled to sell them, do not risk the subject matter since the lapse in your part may attract criminal law , be watchful.