Would it affect my acceptance ratio if I will delete some of my images to the portfolio. I've d been submitting for 3 months now and some of my images are not doing well so I think its better if I just delete them off.

 Are you sure you have good keywording? If you have made sure you correctly keyworded stuff, then removing images from your portfolio I have heard can be beneficial, but I don't do it.. And regarding your question, it depends on what agency you are talking about.. Some it would affect your ratios some it won't.. I would personally just try and figure out what is doing better for you and try to work towards duplicating that into new ideas, don't waste your time trying to nit pick the images you already have up..

What Lisa said plus, you didn't mention where the images are (did you?)  If they are at Dreamstime, acceptance ratio may be important.  It they are at Shutterstock, it doesn't really matter.

Probably best to leave them for at least a year, wherever they may be.