how do you lot allocate more memory to minecraft?

If you play modpacks through CurseForge, Prism or similar, the JVM line in the official launcher doesn't apply. Each of those has its own memory slider in its settings and that's the one that counts.

In the official launcher go to Installations, hover the one you use, click the three dots and Edit, then More Options. In JVM arguments there's a bit that says -Xmx2G. Change the 2 to however many GB you want, like -Xmx4G, and save. Don't go mad with it. Give it roughly half your RAM at most, more than that and Windows starts struggling and the game can actually get worse. 4 to 6 is plenty for vanilla or a light modpack. If you use CurseForge or Prism they have their own memory slider in settings and ignore the launcher value.