Select 3 or 4 of the stems near the center of the plant and remove the remaining ones by clipping them near the crown.
Bundle the chosen stems loosely and stake them in an upright position, using wide cotton tape or use a cord or wire enclosed by plastic tubing or a piece of old garden hose, to avoid chafing the bark.

If you want to train as a standard or tree form, wait a few seasons and then select the largest, straight, upright stem and remove the rest. Prune any lower branches, long whips from upper branches and any other growth from the roots.

They bloom on new seasons growth, so pruning can be done anytime after the flowering period, until spring.

You can root the cuttings, for additional plants. Select limber, not rigid, stems and cut them just below the lowest leaf node, remove all foliage except those leaves at the apex (cut those in half, horizontally, if large) and insert the stems into a well drained pot of sand, perlite and a small amount of compost, loam or potting mix (w/o Fertilizer) and keep it moist.
If your atmosphere is typically low in humidity, you may need to "tent" the pot with a clear plastic bag, secured around the pot with a rubber band or cord. Use stakes to prevent the plastic bag from touching the cuttings. Roots will often begin to form after 4-6 weeks, but I usually leave them to grow for about 6 months, before potting them individually.

If you fertilize, and potted plants usually require some form, you may benefit from your own experiences or seek the advice of your local County Extension Agent.
I use a balanced water soluble type, usually 20-20-20, for seedlings, tissue cultured and cutting grown plants.

Good luck!