first get a two to three gallon pot and prepare your new pot with 4"/5" of soil on the bottom.now build some soil around the edges of the pot as high as you can so your soil in the pot looks like an ice cream cone shape(make sure this is done before you do anything with the seedling).the quicker you transplant the better.if your small pot can be cut then standing next to your prepared pot cut it down the sides with scissors or a stanley.once you have done this hold the small pot sideways with one hand and gently tip it untill your seedling and its rootball and surrounding soil lands in your other hand.dump the cut pot and gently put the seedling and all the surrounding soil you have into your cone shape in the big pot.try and centralise it first time and just sit it in dont push it down.then start burying with the soil you pushed to the side of the pot to give you the cone shape.dont pack the soil just push it over the rootball.once the soil in the pot is level just start layering the soil untill its 2/3/inches from the brim of the pot.and water in if reqd(light spray).and thats you done.
dont worry to much stay cool.its not a human heart your transplanting its just a weed and even if you damage it it will grow again guaranteed.
good luck.
LUDA.