无法更改此图例标题！

我一直试图改变传奇的标题，但没有任何工作。我浏览了这些论坛，人们建议的每一件事都没有起作用（指南，操纵像scale_color_continuous这样的东西，等等）。
另一个问题是geom_point aes命令中的“size”函数显示在图例中（即，它为我的实际数据的形状下的size命令提供了一个形状）。
我已经花了几个小时来解决这些问题，所以任何帮助都将不胜感激。
下面是生成图表的可重复代码：

## Create data frame
Predictor <- c("No", "Yes", "No", "Yes")
TimePoint <- c("Pre", "Pre", "Post", "Post")
value <- c(33, 32, 31, 40)
SE <- c(1.5, 1.5, 1.5, 1.5)
dataframe <- data.frame(Predictor, TimePoint, estimate, SE)

## Define factors and reorder levels of TimePoint
dataframe$TimePoint <- as.factor(dataframe$TimePoint)
dataframe$Predictor <- as.factor(dataframe$Predictor)
dataframe$TimePoint = factor(dataframe$TimePoint, levels = c("Pre", "Post"), ordered = TRUE)

## Create Plot
ggp <- ggplot(data=dataframe, aes(x=TimePoint, y=value, group=Predictor)) +
  geom_errorbar(aes(ymin=value-SE, ymax=value+SE), width=.1) +
  geom_line()+
  geom_point(aes(shape=Predictor, size=2)) +
  coord_cartesian(ylim = c(0, 50)) + ## specifies upper and lower of y
  ylab("Value") +
  xlab("
       Timing")+
  scale_x_discrete(expand = c(0,0.25)) +
  scale_y_continuous(breaks = seq(0, 50, 5), limits = c(0, 50), expand = c(0, 0)) +
  theme_classic() +
  theme(axis.line = element_line(size = .6, colour = "black", linetype=1),         
        axis.text = element_text( angle = 0, color="black", size=18, face=2),
        axis.title.x = element_text(color="black", size=18, face=2),
        axis.title.y = element_text(color="black", size=18, face=2, margin=margin(r=20)))

print(ggp)

我已经尝试了我在这里找到的每一个建议。下面是一些例子：

ggp + scale_color_discrete(name = "New Legend Title")

ggp + labs(color = "New Legend Title")

ggp + scale_fill_discrete(name="New Legend Title")

ggp + guides(col = guide_color(title = "New Legend Title"))

ggp + labs(color = "New Legend Title")