Well, could you provide the name of the tree please? Yellowing usually means you've watered too often, especially important in winter, and/or in a situation with less light than usual, or a tree planted in soil that doesn't drain properly or has become compacted over time, not allowing water to enter the 'pores' of the roots.

I got it as a present but i think its a chinese elm tree. Do tou think repoting would be a good idea?

If it has oval leaves with scalloped edges, it's probably a C. elm (ulmus parvifolia). I can't say whether you should repot or not - you'll have to judge whether the problem is that you're watering too often (do you at least let the top of the soil dry out between times?), and/or your soil is too slow-draining, or what. If it's just watering too often, water a bit (day or two) less often til spring, but if it's because the soil's mostly peaty potting stuff, you do need to repot (and of course need to check if it's rootbound and needs pruning - do you know how to prune bonsai roots?), etc. You can't grow it as a house plant, and depending on where you live (???) it likely should be living outdoors full time year round and won't last long inside, but tell me where you are.

I also have a C. Elm which is indoors this year(Less than optimal conditions, yet unavoidable). I moved in mid december and knowing this was coming I decided it was a nessesary risk to skip a dormant peiod. This time of year is too late to move outdoors it will cause excesive shock to the tree if you are in colder climates. I do however keep mine in the spair bedroom which is currently unheated aside from the fish tank heater of course. The avg. temp is near 55 since heat from other rooms does still get in. The important things dont over water during dormant periods. Dont shock the plant into freezing temps. but do give it the coolest posible dormancy within your home. Try to keep humidity without spraying water directly on the tree and cross your fingers till its warm and you can move the tree out doors. if you are in a warm weather climate move the plant out doors imeadiatly and keep in a semi shaded area untill healthy without over watering. Also when you get a chance post some pics they will help to diagnose problems. Good luck