Replaced the water heater and there is no hot water coming out upsatirs. Downstairs there is hot water coming out but low preasure

No hot water in any plumbing fixture upstairs ?

Did you bleed the system before you turned water back ON ?

Yes we did, on the faucet I get no water what-so-ever but the shower head I get like rain drops only

You have most likely clogged Aerators at sinks and Flow restrictor screens in shower head.

1. Remove shower head and run water w/o it installed. See how much water you get.
2. Remove Aerator from sink spout and run water w/o it. See how much water you get.

I will definitely try that, but what would clog up the aerators? I did nothing but replaced the water heater. (1st time ever changing a water heater)

It is a common problem. Every time you change hot water heater changes in pressure disturb sediment in pipes. These small particles then travel to your fixtures getting lodged in strainers, aerators and flow restrictors. We always take them off at the most distant bathroom before we turn water back ON. That way we don't have to clean them later...

Was I supposed to wait for the heater to warm up before I opened the faucets? Because what I did was connect, fill up with water, bleed, and then open faucets.

The Aerators should have been removed before you fill up - and stay removed during fill up. That's where most of the loose particles travel through pipes.

Understood, Thanks.