How do I cange the water pump

Disconnect battery ground cable.
Drain cooling system.
Remove drive belt, water pump pulley, crankshaft pulley, timing belt outside cover, timing belt and timing belt tensioner.
Remove water pump mounting bolts and nuts, and water pump.
Install water pump on engine block.
Install rubber seals between water pump and oil pump, and between water pump and cylinder head, Fig. 23.
Install timing belt tensioner, timing belt, timing belt outside cover, crankshaft pulley, water pump pulley and drive belt.
Tighten drive belt so it deflects.25-.35 inch on span between water pump pulley and crankshaft pulley.
Install valve cover and air cleaner.
Fill cooling system.
Connect battery ground cable.

Since you had to remove the timing belt in order to replace the water pump, here is how to install the timing belt. (Along with pictures)
To install:

8. Install the tensioner plate to the tensioner.
9. Insert the lug of the tensioner plate into the hole of the tensioner.
10. Install the tensioner, tensioner plate and spring. Do not tighten the tensioner bolt and stud, make the bolt hand tight only.
11. Check that the timing mark on the camshaft timing pulley is aligned with the V mark on the cylinder head cover. If not align the 2 marks by turning the camshaft by be careful not to turn it more than the allowable range.
12. Check that the punch mark on the crankshaft timing belt pulley is aligned with the arrow mark on the oil pump case. If not align the 2 marks by turning the camshaft by be careful not to turn it more than the allowable range.
13. With the 4 marks aligned, install the timing belt on the 2 pulleys in such a way that the arrow marks on the belt (if so equipped) coincide with the rotating direction of the crankshaft. In this state the No. 1 piston is at top dead center of its compression stroke.
14. Install the tensioner spring and spring damper. To allow the belt to be free of any slack, turn the crankshaft 2 rotations clockwise after installing the tensioner spring and damper. After removing the belt slack, first tighten the tensioner stud to 8 ft. Lbs. (11 Nm) and then the tensioner bolt to 20 ft. Lbs. (27 Nm).

As a final check, confirm that both sets of timing marks are aligned properly.

15. Ensure that the seal is between the water pump and the oil pump case. Install the timing belt outside cover. Torque the timing belt cover bolts to 8 ft. Lbs. (11 Nm).
16. Install the crankshaft pulley. Fit the keyway on the pulley to the key on the crank timing belt pulley and tighten the 4 bolts to 8 ft. Lbs. (11 Nm).
17. Lower the vehicle and install the negative battery cable.