How much RAM are you giving Minecraft? It should be less than half, or else Minecraft goes crazy with the memory and does gigantic memory dumps. (Trust me, I have 4 gigs and I still have to use the standard 1 gigabyte allocation for Minecraft.) Try using 7 gigs.
So I should dedicate 7 Gigs to Minecraft through the java arguments correct?
NO! DO NOT!
Seriously though, while you probably need to allocate more RAM, too much is really bad. It forces the computer to deal with more RAM than it needs, causing lag. The most you will ever need to allocate to Minecraft is 4 GB of RAM, and that only for heavily modded Minecraft.
I do have 64bit Java but how do I go about updating it in the launcher
In the new launcher click launch options, then select the profile you want to change, then enable Java executable. Under Java executable, use the folder button to navigate to the 64 bit Java you have installed and select "javaw.exe". You will have to do this each time you update Java.
If you're using a different launcher like the curse/twitch launcher, then settings for Minecraft are under the gear icon, then select Minecraft from the list, select "jar launcher" under launch method and under version, select "always use latest version" and it will find it automatically.
If you're using a different launcher, you will have to find the Java settings elsewhere.
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