The tires are replaceable. I replace mine about every 5 years or so. it looks like the upper wheel may need a new one. There is a raised area on each side of the wheel. the tire needs to ride in between those ribs. The tires are crowned and that crown helps keep the blade centered. The blade looks pretty chooched too. a new blade does wonders for the cut.
Slip knot: is correct and I would NOT suggest taking apart stuff. Hose down all the guides above & under the table with WD40, and blade tensioner. See if things loosen up, there is a very good chance they will.
The guides are there to support the blade after it is tracking. Preventing the blade from shifting rearward when cutting.
So back off the guides and adjust the blade & tire track. One guide rides on the back of the blade, preventing it from moving off-track
The other centers the blade front to rear, or L&R depending on how you are looking at it.
Adding tension to the blade will cause it to walk outboard. This looks like it should be backed off. Not knowing the original owner, the saw blade may be oversized. The manual most likely will have that measurement.
#1 blade & tire
#2 Second life as a metal saw
#3 The blade should be switched between the blocks, just touching no binding, teeth open not covered.