Replacement chainring compatibility
You can use another brand's chainring just fine, provided that the chainrings are replaceable (some cheaper cranksets are made such that all the chainrings are made in one piece). Assuming that is the case, you just need to measure the B.C.D. as shown here, find a chainring with the same BCD and number of bolts and number of teeth and bolt it on (there is a table of common sizes there).  

Based on the bikes direct picture, it looks like it uses 104 mm 4 bolt chainrings, but thats the current version (so check it out yourself) - do the measurement with a ruler as shown in the prior link. EDIT: This may be a different bike - several different models come up on google for the same bike name. Do the measurement with the ruler. 

Here are some directions on replacing the chainring. Note that you may need some tools you don't have (but for the big ring, you might be able to get away without removing the crank) to remove the crank (namely a crank puller; in a pinch you could use a mallet but I wouldn't recommend it).  

Park Tool also has some nice directions on removing and reinstalling the crank, which you'll need to do in this case since its the middle ring. 

Also, wearing out a chainring in 3 years is pretty quick for most people who ride a hybrid - chainrings typically last more than 20000 miles in my experience, even with cheap ones. I also wouldn't bother replacing it until it was causing problems.