Is it ok to allow a video game to use all of the RAM my computer has?

My game was running slow and when I went hunting around in the settings, since my $1,000 gaming pc shouldn't be running slow, I noticed the RAM was limited to 1 gigabyte. If I changed this to 8 gigabytes, the amount of RAM my computer has, would it be bad and if so why?

?2019-08-11T08:06:20Z

What version of Windows?  Which architecture, 32-bit or 64-bit?

Norm F2019-08-11T05:18:42Z

Yes a bad idea. Windows or whatever O/S you are running has routines that are running so they will need RAM.
What are the specs for your game?
What do you mean "you noticed RAM was limited to 1GB"

?2019-08-11T04:13:02Z

If you have a $1000 PC with 8 GB of RAM, consider upgrading to 16 GB or at least 32 GB at most.

Also, post specifications.