My iphone 4 laggs, wifi connection lost frequently and don't connect several times , games jerks a lot , will apple replace my phone4 ?

Basic troubleshooting from the User's Guide is reset, restart, restore (first from backup then as new). Try each of these in order until the issue is resolved.

If this does not resolve the issue, take the device to Apple for evaluation.

Only Apple can say if they will replace the device.

Restore as new, if the problem continues take it back to Apple and demand a resolution.

If it works well for a day or two after restoring as new, then the culprit is not the hardware or iOS, but with an app or apps that are installed on the device.

Are those apps updated to the current versions?

Have you tried installing one of those apps and using the device for a few days to see if the problem occurs, then repeating with each subsequent app?

There is no magic answer here. The device and iOS are not the issue. One of the apps is. The only way to find the culprit is to try installing one at a time with several hours or days in between to see what is causing the issue.

The number of apps is irrelevant.

Just because your friend is not having issues does not magically make it a device issue.

If you are unwilling to do any troubleshooting then there is nothing anyone here can do to assist you.

Are the apps up to date? If not, that may be the culprit.