If Minecraft is arguing with you about RAM allocation, there is a solution: create a batch file with a long list of arguments and pathways and save it somewhere on your computer for later. You can't pin it to the start menu, or even the taskbar.
Minecraft Memory is a simple solution to this. Simply install the program onto your Windows PC and select how much memory you would like to allocate into Minecraft, and the pathway to the Minecraft.exe launcher. The program will save these two snippets of information and launch the game client with however much memory you asked for ready and waiting.
This program is built upon request that the default launcher does not always fulfill the task of reserving memory unto itself, and cuts out having to make batch files and shortcuts to them, as well as any confusion to new or younger audiences.
Note: You cannot allocate more memory than your system has. If you are on a 64-bit OS, you must have 64-bit Java installed. This program is also 32-bit OS compatible. Java v7 required.
You should probably add to the note at the bottom, that some of the memory is reserved for the OS and stuff... so if you have 4G of RAM, you really should only allocate like 2-3...
Also, I've heard that because of the way Java works, just throwing more memory at it, won't do that much, performance relies much more on your processor, and GPU...
Most people should already know how to allocate more memory if they are doing this and don't need that tip. This is to fix a known problem when people have already tried using minecraft to allocate the memory. As well as the more RAM you have the larger of a LAN world you can run and also texture packs and shaders use a lot more RAM than regular Minecraft so it's necessary.