1. You might be lucky and find there's enough slack in the existing pipes, once you take the current radiator off, to reach the new position.
2. Are you sure the distance of the pipes from the wall will be the same for the old and new? If not its more complicated.
3. If pipes are copper:
3a. Then if you can get at the pipes under the floor, cut the existing and insert a short but two inch longer length of pipe using a straight connector.
3b. If you can't get under floor, do as 3a but above floor.
4. If pipes are plastic:
4a. Identify make and use pipe / fittings fro same manufacturer.
4b. If you can get under floor, cut pipes and use new pipe and elbow or straight connector to new piece to existing.
4c. If you can't get under floor, use a brass or chrome compression straight connector. Far from ideal as is will show.