Make sure that you copy the advice given on how to install the mod and its patches in the proper order. The Bear's Pit is an amazing location for all things Jagged Alliance. Consulting it will almost always lead to whatever help one's looking for. The community's tight and very happy to help, as long as one asks nicely!
Silkie341: 1.13 allows you to change resolutions but you do need to edit the ini file IIRC.
Zammy: How should I edit it?
Assuming you have a correct installation of JA2 1.13 (and not of UB, I don't think there is a 1.13 version of UB), the JA2.ini will contain the following lines ;************************************************************************************************************* ***************** ; Select the screen resolution of the game. ; 0 ... 640x480 ; 1 ... 800x600 ; 2 ... 1024x768 ;************************************************************************************************************* *****************
SCREEN_RESOLUTION = 1
Change the SCREEN_RESOLUTION = 1 to the resolution you want.