This modpack requires Java 7 (preferrably latest version of 8) 64 bit and at LEAST 2.5 GB of memory!
If your computer is not capable of getting Java 64 bit and/or does not have enough memory then I am afraid you are out of luck.
Type in the modpack name (Ultra Modded-Survival) or paste the following url into the search box.
Finally, click Install at the bottom right of the launcher after you select Ultra Modded-Survival from the list on the left. The launcher will handle everything else!