Reddit mentions of Pentek SW-2 Standard Housing Wrench

Both the filters unscrew. Do you have the [wrench] (http://www.amazon.com/gp/aw/d/B003VT5GCE/ref=mp_s_a_1_1?qid=1425432521&sr=8-1&keywords=water+filter+wrench&pi=AC_SX200_QL40&dpPl=1&dpID=31%2BYNMNwO%2BL&ref=plSrch) that came with it? They help. Make sure you bleed off the pressure as well. Often a button on top of the assembly.

That's an industry standard housing size for filters and it looks like the size that some people describe as 10" x 2.5" and some as 9-3/4 x 2-7/8. You can (with water off) open it up to remove and measure the existing cartridge. You can also run it with no filter cartridge in it if water flow volume is currently too low and that's the immediate problem.

Instruction video on replacing the filter is here: play this video at double speed^☨. If the previous owners have not left the "wrench" and it won't come off just by gripping and turning, you can use an automotive strap wrench or order a replacement wrench cheaply

I used to replace mine at the local big box store, you will see that each model has a slightly different menu of what it controls. For city water, most people want the chlorine removed, but in some places it is worth spending much more on ones that will remove lead, arsenic, or some other contaminant of concern also. I've found online purchase of Pentek EP-10 or equivalent much cheaper than local purchase.

Whoever put the filter there wanted it for some reason, so if you can figure out the reason, that will inform your choice of replacement cartridge. You may consider asking the neighbors if they filter their drinking water and why. In the meantime, just put whatever is cheap that fits, and you will restore adequate flow volume to the sink and dishwasher.

^☨ (on youtube if you click the gear icon at the lower right it will allow you in "settings" to change the speed of playback. Pitch is unaffected.)