I need to replace my alternator and do not see how to loosen and then retension the belt

all of those units will have a bolt in a slot adjustment
loosen the bolt and move the unit so that the belt gets loose
fit new belts and then retension the belt and tighten the bolt

yes you have to loosen of the big nut as that is what maintains the pulley position after adjustment
retension after tensioning the belt

if you mean the belt that drives the alternator /water pump/power steering pump etc the adjustment for the belt is at the idler pulley. loosen off the nut holding on the pulley and behind the pulley ther should be a long threaded bolt that moves the pulley up or down. When finished retension the idler pulley nut

Find the idler that has an adjuster screw/bolt behind it. Loosen of the nut holding on the pulley Turn the adjuster until the belt is loose. Remove belt and install new belt going around each pulley correctly. Retension adjuster and when correct tension is achieved retighten the nut on the pulley

replace alternator belt.you need to loosen alternator upper and lower belt then push alternator forward to slip off drive belt.if you have the prizim GSI. you need to raise and support the vechicle safely.remove the power steering and air conditioning drive belts.then loosen the lower mounting bolt and nut from the alternator bracket.then remove the alternator drive belt.

The only way to replace an alternator drive belt that is on an inside pulley is to remove the outer belts before the inner one can be fitted.
To fit inner belt, loosen the adjusting clamp and mounting bolts on the units that tension the outer belts such as the aircon compressor and power steering units and moove them to loosen the belts and then remove these belts. Once these belts are off, check them for wear and cracking of the rubber on the inside surface and if suspect it would pay to replace them as well. Loosen clamp and mounting bolts on the alternator, if not already done so, and moove alternator so that alternator belt can be fitted.
Retension alternator belt and tighten clsmping and mounting bolts Refit other belts in turn and tension and tighten clamping and mounting bolts.
Correct tension is when belt is pushed on the longest run between pulleys with a 10 Kg force. Belt should deflect a maximum of 8 mm.

check the tension. cheap belts will stretch. if after you retension them (especially the alternator belt) you may need to replace them with BANDO or OEM belts.

FOR THE 3.0L ENGINE IF YOU REPLACE AC BELT LOOSEN TOP IDLER PULLEY CENTER BOLT. IF YOU REPLACING ALTERNATOR AND WATER PUMP BELT LOOSEN ALTERNATOR ADJUSTMENT BOLT AND PIVOT BOLT.IF REPLACING POWER STEERING PUMP BELT LOOSEN POWER STEERING PUMP ADJUSTMENT BOLT AND MOUNTING BOLTS.****** FOR THE 2.4L ENGINE TO REMOVE POWER STEERING BELT LOOSEN TOP IDLER PULLEY.FOR ALTERNATOR AND WATER PUMP BELT LOOSEN ALTERNATOR ADJUSTER BOLT, PIVOT AND MOUNTING BOLTS.FOR AC COMPRESSOR LOOSEN LOWER IDLER PULLEY.

If by frozen you mean that it is very difficult to move far enough to loosen the belt and then won't spring back to retension the belt then the tensioner assembly will need to be replaced. Not a real uncommon problem and I see this happen to tensioners on all brands of vehicles. Not to hard to replace. Hope this helps!

loosen the bolt that is holding the adjuster of the alternator. loosen the belt by pulling it and the alternator would slide in. remove and replace the belt.

do the reverse on installation.

remember to tighten all bolts of the adjuster and alternator after tightening the belt.

tnx 4 using fixya,

drcool