I have two instances of SuiteCRM, the clients had told that SuiteCRM is slow (about 10 seconds), both are in different servers, so i want to know what configuration i can do to improve the performance and decrease the response time of the instances, maybe editing httaccess or cache module to apache.
The advice given above is good (and do tell us your versions of everything, sometimes that gives us clues).
Then you can also provide some notion of how big are your servers, and how big is your database.
And you can go into phpMyAdmin and check the size of individual tables. Most of the problems with bad performance I’ve seen recently on these forums are caused by something growing disproportionately large on the database.