Hi and welcome to ExTS
You may be interested in this review:
http://www.pcpro.co.uk/reviews/graphics-cards/355276/ati-radeon-hd-5450
It says "no good for gaming".
"In fact, the only area where it fails to impress is in the latest games. It motored through our Low-quality Crysis test at 57fps, but a score of 17fps in our Medium-quality test, run at a resolution of 1,280 x 1,024, puts paid to any serious gaming prospects."
I am not a gamer - but I do think that you are going to have to invest a little more cash if you are going to be happy with the results when gaming.
Just as an added extra...
Depending upon which video card you opt for you may need to upgrade your PSU.
It really depends on what you have installed at the moment and the specific card you go for.