I've routed my PCB but had to change the minimum keepout rules which means I'll now have a lot of DRC errors - most tracks are too closely placed together and that would violate the new keepout rule.
However, I can see the errors only when I route a track. 
Is there a way to see all DRC violations at a glance? I'm sure there's a better way of doing it than selecting each track individually.
If you have your rules set up properly, all you have to do is go to Tools --> Design Rule Check and click "Run Design Rule Check" at the bottom left of the pane. I tend to use the shortcut T-D-Enter and it does all of the above in just three keystrokes. This will list all of the design errors, provided you told the DRC to check them in the batch check. If you want to change what rules it looks for, go to Tools --> Design Rule Check (or shortcut T-D) and in the left-pane, under "Rules To Check", you can select your category and which rules you want the DRC to check.
Go to Tools : DRC check. Make sure to enable all applicable errors in a long hierarchical list. Then run Batch DRC. It has to mark all violations in green color and make a list of violations in Messages window.
By the way, you can automatically change the width of certain traces using Altium scripts.
