Nokia 6303 classic
Memory capacity problem

I purchased mobile set on 7.11.2009. Memory capacity as displayed in the set is 6.8 MB against 17MB displayed in friend's Nokia 6303classic mobile set. The show room staff could not give convincing reply for query made in person on 02.12.2009. The answer is confusing. I was told that if memory capacity increased the set will develop problems and I may not be able to use it properly. Please be kind enough to clarify the doubt and do the needful.

INVOICE NO. SI/5270, DT.07.11.2009 FOR RS. 7266/-

6303CLASSIC IN MATT BLACK SP: NOKIA N6303C

358005038259922

NOKIA STORES ROCKY AGENCIES CH-600 018