How do I change the sanding belt on my 7447 belt sander

please be more specific!!
guessing - bench top disc/belt sanders' discs usually use stick on backed sand paper discs ;)

Google the model number and "manual".

The 7447 does not have a release lever. To change the belt, you must release tension of the rollers by pushing the front roller straight back until you hear it click and lock in position to change paper. Remove old paper and replace with new paper. Make sure if new paper has directional arrows to install properly.
Now you must release the front roller to put tension on paper. To do this push the front roller from the side that has the adjustment screw. This will release the front roller and allow it to go back into position. Be careful as it pops back quickly and with some force.
Turn on sander and adjust centering of paper with adjustment screw found near the front and side of sander.

there should be a lever that will loosen the tention on the belt so you can get it off. be sure to put the new belt on with the arrows facing the rotation (some sanding belts do not need to be oriented this way, but check) otherwise the belt will come apart after a few rotations.

To change belt:
1) Put front roller on floor and push down until roller locks back.
2) Put on new sand paper.
3) Loosen tracking screw until front roller is released.
4) With sander running, use tracking screw to center belt.

is it a B & D 3x21 belt saNDER. iF SO, PUST THE REAR DRIVE WHEEL FORWARD UNTIL IT CATCHES, PUT THE SANDING BELT ON, THEN RELEASE THE CATCH WITH A LONG SCREWDRIVER ANDIT WILL SNAP BACK INTO PLACE. hOPE THIS HELPS

I have one of those and I just smack the front roller ahead with a brass or plastic hammer. I hit the movable bracket that the roller is attached to. It takes a pretty stout whack to do it though. hope this helps you

All sander will have two adjustments. The first is to release the sanding belt by retracting the position of one of the rollers. The second adjustment moves one of the rollers belt tension from side to side. The roller angular position is changed, sometime by a single knob or screw, and sometimes by two separate adjusting screws.

Check and see if the pulleys on the sander are not glazed this somtimes will cause the belt to slip. Give them a good cleaning. If this does not help there is a good chance the spring on the belt tensioner is weak and need changed.

Hop this helps