Not sure what it is but it is pot-bound ie the pot is now too small for the roots, and the pot is a totally unsuitable shape.
Ideally you would plant it/them in the ground in a suitable compost, once someone has decided what it is, or in a larger pot that does not have a narrow neck. It looks as if you may have to smash the existing pot to remove the shrub.

Looks like Nerium Oleander. It needs the sunniest spot in your garden, near a south facing wall and sheltered from winds. I would say pot up rather than in the ground as they are not that hardy: certainly fast draining moist soil in summer and winter.

Agree with Botanic, it is Nerium and it does need potting up into something larger, evidenced by the smaller leaves its producing. Which gives you an immediate problem - you're never going to get it out of that pot intact because its narrower at the top than lower down, you'll either have to break the pot or sacrifice the plant. This type of pot is really only useful for annual plants, or simply stood around for decorative purposes.

These can survive in the ground, but only in very sheltered, preferably south facing gardens, in the lee of a wall, or in paved areas (because paving reflects and holds heat). One garden (in London) I know has one at the front, south facing, against a wall, and its enormous, has to be cut back so it doesn't block the pavement. It still had some flowers in early December last year...