Has it just finished flowering?

If it has then just leave it to die back on its own!

When did you last feed it, like most bulbs they want feeding prior to dieback so that they can charge their batteries for the next flowering season!

Have a look here;

http://www.thegardenersalmanac.co.uk/Data/Amaryllus/Amaryllus.htm

They don't like root disturbance, but this one looks as though it could do with a bigger pot. Try not to let it know you are moving it!
Don't cut the leaves off as they are feeding up the bulb. This looks like a very young plant and may not flower again for a year or two, but feed it while it has leaves and then when summer comes turn the pot on one side (leaves or not!) and keep it quite dry until mid autumn. Then water again. If it is going to flower the bud will appear first, so if you get leaves firs, just sigh and wait another year!

It was given to me last Christmas and flowered magnificently. I then put it in the conservatory, and then in the summer, I put it out doors and kept it moist. But I haven't fed it.
I've just brought it in.
I thought it needed a larger pot. Shall I just use regular potting compost?

Yes that will be fine but do try not to disturb it any more than necessary. The dry period is important.